gbm/dri: Remove erroneous assert
The user is allowed to pass a list of modifiers including DRM_FORMAT_MOD_INVALID, meaning that the user is OK with implicit modifiers. Since merging the DRI interfaces, this assert that we are never returning an implicit modifier is unnecessary and also wrong. It was originally added to be super-safe, but we now know that our drivers work very well with modifiers, so don't need it.
Fixes: 0b16d7eb ("dri: Allow INVALID for modifier-less drivers")
Closes: #11591 (closed)
Edited by Daniel Stone