radeonsi/nir: Remove hack for builtins

radeonsi/nir: Remove hack for builtins

We now bounds check properly in the uniform loading fast path, so
there's no need to disable it by pretending there are other UBO bindings
in use. The way this looks at the variable name was causing problems
when two piglit shaders, one with a name that triggered the hack and one
that didn't, got hashed to the same thing after stripping out the names.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>