trees: also remove single-tree repo/p/

single-tree repos were not previously cached, but now
they are and they have to be handled.

this, as also alluded to in the previous commit, is done
when preparing release archives (XBMK_RELEASE=y)

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/trees

@@ -38,8 +38,7 @@ main()
 	[ -z "$_f" ] && $err "missing flag (-m/-u/-b/-c/-x/-f/-s/-l/-n)"
 	[ -z "$project" ] && for p in $(ls -1 config/git); do
 		./update trees $_f "$p" || $err "!./update trees $_f $p"
-		[ "$XBMK_RELEASE" != "y" ] || singletree "$p" || \
-		    x_ rm -Rf "repo/$p"; continue
+		[ "$XBMK_RELEASE" != "y" ] || x_ rm -Rf "repo/$p"; continue
 	done && return 1
 
 	[ -f "config/git/$project/pkg.cfg" ] || $err "'$project' not defined"