cogl/egl: Don't log "EGL color depth" anymore
Since e437c854 config
no longer represents the current config
but rather the fallback config that in most cases isn't being used. So
reporting on its attributes is now misleading.
Logging the current depth can instead now be done with MUTTER_DEBUG=kms and grepping for "KMS: Using GBM format".
Closes: #3174 (closed)