xbps-src: remove WIP repo delta support.

- it never worked correctly
- it's WIP and looks like it will be stalled forever
- won't be necessary anymore with xbps-0.42

common/hooks/pre-pkg/01-xdelta_repolist.sh

@@ -1,12 +0,0 @@
-# this hook marks files which are about to change for generating vcdiffs
-
-hook() {
-	[ -z "$XBPS_REPO_DELTAS" ] && return 0
-	type -P xdelta3 > /dev/null || return 0
-
-	# create links to preserve old versions of repodata
-	find $XBPS_REPOSITORY -name "${XBPS_TARGET_MACHINE}-repodata" | while read; do
-		( rm "${REPLY}.genVcdiff" 2>/dev/null ) || true
-		cp "${REPLY}" "${REPLY}.genVcdiff"
-	done
-}