build: Depend on Cogl 1.15.9

The laxy texture allocation has been removed from Cogl 1.15, so we need
to depend on the new developers snapshot.
Revert "clutter-offscreen-effect: Allocate the cogl texture directly"

This reverts commit 180e7d74f3325731ac5e91350233c26200a44fd7.

The lazy texture allocation is gone in Cogl 1.15.9.
Release Clutter 1.15.92 (snapshot)
Post-release version bump to 1.15.93