Wayland: Reintroduce log output for wl_shm fallback

Commit 137966a6293b50f6b248d130a2e36e67df49335e added additional debug output when the wl_shm backend was automatically selected because wayland-egl (or something else) could not be initialized. This was so that users would be aware that they were running on an unoptimal setup and fix the core issues for this.

But the side effect was that when testing Wayland on desktop, with the default binary builds from Qt (which depend on the wl_shm fallback), the Wayland plugin would claim it did not support OpenGL whereas this did not happen before.

A further side effect of this was that Qt Quick would default to the software renderer, which has limited support for shader effects and which caused Qt 3D applications to crash.

Since this was not the intended effect of the commit, it was reverted: af3976e5e788392ab2b0299c11036c18493d8d40

Next step is to reintroduce the warnings without the behavioral change.