Fixes for make dist

Reduce the usage of EXTRA_DIST. If files are conditionally included in
_SOURCES, _HEADERS etc, automake is smart enough to dist all files that
could possibly be included, but this does not apply to EXTRA_DIST,
resulting in make dist depending on the configuration.

Add some files that were missing altogether in various Makefile's.

The changes to disted files in this commit (excluding deleted files):

+./cmd/zed/agents/README.md
+./etc/init.d/README.md
+./lib/libspl/os/freebsd/getexecname.c
+./lib/libspl/os/freebsd/gethostid.c
+./lib/libspl/os/freebsd/getmntany.c
+./lib/libspl/os/freebsd/mnttab.c
-./lib/libzfs/libzfs_core.pc
-./lib/libzfs/libzfs.pc
+./lib/libzfs/os/freebsd/libzfs_compat.c
+./lib/libzfs/os/freebsd/libzfs_fsshare.c
+./lib/libzfs/os/freebsd/libzfs_ioctl_compat.c
+./lib/libzfs/os/freebsd/libzfs_zmount.c
+./lib/libzutil/os/freebsd/zutil_compat.c
+./lib/libzutil/os/freebsd/zutil_device_path_os.c
+./lib/libzutil/os/freebsd/zutil_import_os.c
+./module/lua/README.zfs
+./module/os/linux/spl/README.md
+./tests/README.md
+./tests/zfs-tests/tests/functional/cli_root/zfs_clone/zfs_clone_rm_nested.ksh
+./tests/zfs-tests/tests/functional/cli_root/zfs_send/zfs_send_encrypted_unloaded.ksh
+./tests/zfs-tests/tests/functional/inheritance/README.config
+./tests/zfs-tests/tests/functional/inheritance/README.state
+./tests/zfs-tests/tests/functional/rsend/rsend_016_neg.ksh
+./tests/zfs-tests/tests/perf/fio/sequential_readwrite.fio

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10501

contrib/dracut/02zfsexpandknowledge/Makefile.am

@@ -15,10 +15,4 @@ $(pkgdracut_SCRIPTS):%:%.in
 		-e 's,@sysconfdir\@,$(sysconfdir),g' \
 		$< >'$@'
 
-# Double-colon rules are allowed; there are multiple independent definitions.
-clean-local::
-	-$(RM) $(pkgdracut_SCRIPTS)
-
-# Double-colon rules are allowed; there are multiple independent definitions.
-distclean-local::
-	-$(RM) $(pkgdracut_SCRIPTS)
+CLEANFILES = $(pkgdracut_SCRIPTS)

contrib/dracut/90zfs/Makefile.am

@@ -37,6 +37,4 @@ $(pkgdracut_SCRIPTS) $(pkgdracut_DATA) :%:%.in
 		-e 's,@mounthelperdir\@,$(mounthelperdir),g' \
 		$< >'$@'
 
-# Double-colon rules are allowed; there are multiple independent definitions.
-distclean-local::
-	-$(RM) $(pkgdracut_SCRIPTS) $(pkgdracut_DATA)
+CLEANFILES = $(pkgdracut_SCRIPTS) $(pkgdracut_DATA)

contrib/pam_zfs_key/Makefile.am

@@ -14,5 +14,4 @@ pam_zfs_key_la_LDFLAGS = -version-info 1:0:0 -avoid-version -module -shared
 
 pam_zfs_key_la_LIBADD += -lpam $(LIBSSL)
 
-pamconfigs_DATA = zfs_key
-EXTRA_DIST = $(pamconfigs_DATA)
+dist_pamconfigs_DATA = zfs_key