Trim excess shellcheck annotations. Widen to all non-Korn scripts

Before, make shellcheck checked
  scripts/{commitcheck,make_gitrev,man-dates,paxcheck,zfs-helpers,zfs,
           zfs-tests,zimport,zloop}.sh
  cmd/zed/zed.d/{{all-debug,all-syslog,data-notify,generic-notify,
                 resilver_finish-start-scrub,scrub_finish-notify,
                 statechange-led,statechange-notify,trim_finish-notify,
                 zed-functions}.sh,history_event-zfs-list-cacher.sh.in}
  cmd/zpool/zpool.d/{dm-deps,iostat,lsblk,media,ses,smart,upath}
now it also checks
  contrib/dracut/{02zfsexpandknowledge/module-setup,
                  90zfs/{export-zfs,parse-zfs,zfs-needshutdown,
                         zfs-load-key,zfs-lib,module-setup,
                         mount-zfs,zfs-generator}}.sh.in
  cmd/zed/zed.d/{pool_import-led,vdev_attach-led,
                 resilver_finish-notify,vdev_clear-led}.sh
  contrib/initramfs/{zfsunlock,hooks/zfs.in,scripts/local-top/zfs}
  tests/zfs-tests/tests/perf/scripts/prefetch_io.sh
  scripts/common.sh.in
  contrib/bpftrace/zfs-trace.sh
  autogen.sh

Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12042

tests/zfs-tests/tests/functional/cli_root/zpool_events/zpool_events_duplicates.ksh

@@ -102,8 +102,7 @@ function do_dup_test
 
 		# Read the file a few times to generate some
 		# duplicate errors of the same blocks
-		# shellcheck disable=SC2034
-		for i in {1..15}; do
+		for _ in {1..15}; do
 			dd if=$FILEPATH of=/dev/null bs=128K > /dev/null 2>&1
 		done
 		log_must zinject -c all

tests/zfs-tests/tests/perf/scripts/prefetch_io.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# shellcheck disable=SC1004
 
 #
 # This file and its contents are supplied under the terms of the
@@ -24,38 +25,37 @@ zfs_kstats="/proc/spl/kstat/zfs"
 
 function get_prefetch_ios
 {
-        typeset -l data_misses=`awk '$1 == "prefetch_data_misses" \
-            { print $3 }' $zfs_kstats/arcstats`
-        typeset -l metadata_misses=`awk '$1 == "prefetch_metadata_misses" \
-            { print $3 }' $zfs_kstats/arcstats`
-        typeset -l total_misses=$(( $data_misses + $metadata_misses ))
+	typeset -l data_misses="$(awk '$1 == "prefetch_data_misses" \
+	    { print $3; exit }' "$zfs_kstats/arcstats")"
+	typeset -l metadata_misses="$(awk '$1 == "prefetch_metadata_misses" \
+	    { print $3; exit }' "$zfs_kstats/arcstats")"
+	typeset -l total_misses=$(( data_misses + metadata_misses ))
 
-        echo $total_misses
+	echo "$total_misses"
 }
 
 function get_prefetched_demand_reads
 {
-	typeset -l demand_reads=`awk '$1 == "demand_hit_predictive_prefetch" \
-	    { print $3 }' $zfs_kstats/arcstats`
+	typeset -l demand_reads="$(awk '$1 == "demand_hit_predictive_prefetch" \
+	    { print $3; exit }' "$zfs_kstats/arcstats")"
 
-	echo $demand_reads
+	echo "$demand_reads"
 }
 
 function get_async_upgrade_sync
 {
-	typeset -l sync_wait=`awk '$1 == "async_upgrade_sync" \
-	    { print $3 }' $zfs_kstats/arcstats`
+	typeset -l sync_wait="$(awk '$1 == "async_upgrade_sync" \
+	    { print $3; exit }' "$zfs_kstats/arcstats")"
 
-	echo $sync_wait
+	echo "$sync_wait"
 }
 
 if [ $# -ne 2 ]
 then
-	echo "Usage: `basename $0` <poolname> interval" >&2
+	echo "Usage: ${0##*/} poolname interval" >&2
 	exit 1
 fi
 
-poolname=$1
 interval=$2
 prefetch_ios=$(get_prefetch_ios)
 prefetched_demand_reads=$(get_prefetched_demand_reads)
@@ -64,19 +64,19 @@ async_upgrade_sync=$(get_async_upgrade_sync)
 while true
 do
 	new_prefetch_ios=$(get_prefetch_ios)
-	printf "%u\n%-24s\t%u\n" $(date +%s) "prefetch_ios" \
-	    $(( $new_prefetch_ios - $prefetch_ios ))
+	printf "%u\n%-24s\t%u\n" "$(date +%s)" "prefetch_ios" \
+	    $(( new_prefetch_ios - prefetch_ios ))
 	prefetch_ios=$new_prefetch_ios
 
 	new_prefetched_demand_reads=$(get_prefetched_demand_reads)
 	printf "%-24s\t%u\n" "prefetched_demand_reads" \
-	    $(( $new_prefetched_demand_reads - $prefetched_demand_reads ))
+	    $(( new_prefetched_demand_reads - prefetched_demand_reads ))
 	prefetched_demand_reads=$new_prefetched_demand_reads
 
 	new_async_upgrade_sync=$(get_async_upgrade_sync)
 	printf "%-24s\t%u\n" "async_upgrade_sync" \
-	    $(( $new_async_upgrade_sync - $async_upgrade_sync ))
+	    $(( new_async_upgrade_sync - async_upgrade_sync ))
 	async_upgrade_sync=$new_async_upgrade_sync
 
-	sleep $interval
+	sleep "$interval"
 done