autogen.sh: remove workaround for automake <1.14, needed for EL <=7

Ultimately this is a revert of 779ac93, which according to
@nabijaczleweli is to paper over automake <1.14's lack of
%reldir% support.

As I understand it, EL8 is the lowest current build target.

Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Joseph Holsten <joseph@josephholsten.com>
Closes #17878

autogen.sh

@@ -1,62 +1,3 @@
 #!/bin/sh
-[ "${0%/*}" = "$0" ] || cd "${0%/*}" || exit
 
-# %reldir%/%canon_reldir% (%D%/%C%) only appeared in automake 1.14, but RHEL/CentOS 7 has 1.13.4
-# This is an (overly) simplistic preprocessor that papers around this for the duration of the generation step,
-# and can be removed once support for CentOS 7 is dropped
-automake --version | awk '{print $NF; exit}' | (
-	IFS=. read -r AM_MAJ AM_MIN _
-	[ "$AM_MAJ" -gt 1 ] || [ "$AM_MIN" -ge 14 ]
-) || {
-	process_root() {
-		root="$1"; shift
-
-		grep -q '%[CD]%' "$root/Makefile.am" || return
-		find "$root" -name Makefile.am "$@" | while read -r dir; do
-			dir="${dir%/Makefile.am}"
-			grep -q '%[CD]%' "$dir/Makefile.am" || continue
-
-			reldir="${dir#"$root"}"
-			reldir="${reldir#/}"
-
-			canon_reldir="$(printf '%s' "$reldir" | tr -C 'a-zA-Z0-9@_' '_')"
-
-			reldir_slash="$reldir/"
-			canon_reldir_slash="${canon_reldir}_"
-			[ -z "$reldir" ] && reldir_slash=
-			[ -z "$reldir" ] && canon_reldir_slash=
-
-			echo "$dir/Makefile.am" >&3
-			sed -i~ -e "s:%D%/:$reldir_slash:g"       -e "s:%D%:$reldir:g" \
-			        -e "s:%C%_:$canon_reldir_slash:g" -e "s:%C%:$canon_reldir:g" "$dir/Makefile.am"
-		done 3>>"$substituted_files"
-	}
-
-	rollback() {
-		while read -r f; do
-			mv "$f~" "$f"
-		done < "$substituted_files"
-		rm -f "$substituted_files"
-	}
-
-
-	echo "Automake <1.14; papering over missing %reldir%/%canon_reldir% support" >&2
-
-	substituted_files="$(mktemp)"
-	trap rollback EXIT
-
-	roots="$(sed '/Makefile$/!d;/module/d;s:^\s*:./:;s:/Makefile::;/^\.$/d' configure.ac)"
-
-	IFS="
-"
-	for root in $roots; do
-		root="${root#./}"
-		process_root "$root"
-	done
-
-	set -f
-	# shellcheck disable=SC2086,SC2046
-	process_root . $(printf '!\n-path\n%s/*\n' $roots)
-}
-
-autoreconf -fiv && rm -rf autom4te.cache
+autoreconf -fiv "$(dirname "$0")" && rm -rf "$(dirname "$0")"/autom4te.cache