vulkan: clean up _mesa_locale_init/fini usage.

The resulting locale is only used for GL program / GLSL lexing and hence not used in Vulkan.

init/fini do not refcount and hence this is problematic when there are multiple vulkan instances.

This has been massively cargo culted from anv (my fault ...).

I tested by putting an abort on _mesa_strtod/_mesa_strtof and got zero crashes with radv on a recent (~past few weeks) vulkan-cts.