Simplify some GLSL shader loading code

[VReaperV]

Make somewhat messy code I noticed while working on #1105 and subsequent prs into something more readable.

Merge the two branches in GLShaderManager::buildPermutation() into one since they were doing essentially the same thing. Change some variable names to avoid confusion between shader and shader programs, fixed some formatting like whitespaces in [] and missing {} in if statements. Removed a redundant namespace in function call.

There is technically a slight difference in that compute shaders may be loaded even if deformIndex is > 0, but I don't think that really matters.