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

contrib/initramfs/hooks/zfs.in

@@ -26,7 +26,7 @@ fi
 
 # We use pthreads, but i-t from buster doesn't automatically
 # copy this indirect dependency: this can be removed when buster finally dies.
-for libgcc in $(find /lib/ -type f -name libgcc_s.so.[1-9]); do
+find /lib/ -type f -name "libgcc_s.so.[1-9]" | while read -r libgcc; do
 	copy_exec "$libgcc"
 done
 

contrib/initramfs/scripts/local-top/zfs

@@ -1,18 +1,11 @@
 #!/bin/sh
-PREREQ="mdadm mdrun multipath"
+# shellcheck disable=SC2154
 
-prereqs()
-{
-        echo "$PREREQ"
-}
 
-case $1 in
-# get pre-requisites
-prereqs)
-        prereqs
+if [ "$1" = "prereqs" ]; then
+        echo mdadm mdrun multipath
         exit 0
-        ;;
-esac
+fi
 
 
 #
@@ -20,10 +13,10 @@ esac
 #
 message()
 {
-        if [ -x /bin/plymouth ] && plymouth --ping; then
-                plymouth message --text="$@"
+        if plymouth --ping 2>/dev/null; then
+                plymouth message --text="$*"
         else
-                echo "$@" >&2
+                echo "$*" >&2
         fi
         return 0
 }