mesa: Back out an accidental change I had in a VC4 commit.
mesa: Back out an accidental change I had in a VC4 commit.

This was a hack as part of debugging some glamor-on-GLES2 behavior that
ended up being an xserver bug.  I suspect we can just flip this extension
on for GLES2, but the spec says it requires 3.1.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler