Remove necessity of sampler map

[alan-baker]

Currently to support literal samplers, clspv requires a sampler map to be specified. Since the intervention of the descriptor map this is no longer necessary.

Support for the sampler map will be removed in the following steps:

1. Deprecate the option a. Issue a warning on its use b. Add support for generating literal samplers without the sampler map
2. (Later) remove the option altogether

The internal representation of samplers will use the data mask instead of the index into the sampler map.