gluon-core: remove support for incremental upgrade scripts

As we don't have any older gluon versions so far, and hope to be able to do all
upgrades with invariant scripts, remove the code for now.

If we ever see the need to add such upgrade scripts, we can just re-add this.

package/gluon-core/files/etc/uci-defaults/zzz-gluon-upgrade

@@ -45,17 +45,6 @@ do_component() {
 			else
 				do_dir initial
 			fi
-		else
-			local v
-
-			for v in *; do
-				[ "$v" != initial -a "$v" != invariant -a "$v" != legacy ] || continue
-
-				# The return value of opkg compare-versions is negated
-				if ! opkg compare-versions "$v" '>>' "$oldversion"; then
-					do_dir "$v"
-				fi
-			done
 		fi
 
 		do_dir invariant