Revert "egl/glx: add fallback for zink loading"

This reverts commit 2569215f.

Conflicts: src/egl/main/eglapi.c src/glx/glxext.c

It broke the fallback to swrast in some cases where zink can't work.

Closes: #7333 (closed) Fixes: 2569215f ("egl/glx: add fallback for zink loading")