Revert "Implement a cpio emulation in git-merge.sh for Windows."

This reverts commit 8b9de09319.
git-merge does not use cpio anymore.

git-merge.sh

@@ -38,24 +38,6 @@ use_strategies=
 allow_fast_forward=t
 allow_trivial_merge=t
 
-# Fix some commands on Windows
-case $(uname -s) in
-*MINGW*)
-	# there's no cpio; emulate with tar
-	cpio () {
-		case "$*" in
-		"-0 -o")
-			tar --create --file=- --null --files-from=-
-			;;
-		"-iuv")
-			tar xvf -
-			;;
-		*)	die "internal error: unexpected cpio $*";;
-		esac
-	}
-	;;
-esac
-
 dropsave() {
 	rm -f -- "$GIT_DIR/MERGE_HEAD" "$GIT_DIR/MERGE_MSG" \
 		 "$GIT_DIR/MERGE_STASH" || exit 1