nir: Drop the vs_inputs_dual_locations option

nir: Drop the vs_inputs_dual_locations option

It was very inconsistently handled; the only things that made use of it
were glsl_to_nir, glspirv, and nir_gather_info.  In particular,
nir_lower_io completely ignored it so anyone using nir_lower_io on
64-bit vertex attributes was going to be in for a shock.  Also, as of
the previous commit, it's set by every driver that supports 64-bit
vertex attributes.  There's no longer any reason to have it be an option
so let's just delete it.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>