Revert "Vulkan: Use VK_NV_glsl extension where available, and skip glslang"

This reverts commit d23fd17e1a.

Dynamic sampler indexing is broken in VK_NV_glsl as of 385.41. The
performance gap doesn't seem to be as wide with the updated driver, so
to save maintaining two code paths, it's easier to just drop the
extension support completely.

Source/Core/VideoBackends/Vulkan/ShaderCompiler.h

@@ -19,19 +19,19 @@ using SPIRVCodeVector = std::vector<SPIRVCodeType>;
 
 // Compile a vertex shader to SPIR-V.
 bool CompileVertexShader(SPIRVCodeVector* out_code, const char* source_code,
-                         size_t source_code_length);
+                         size_t source_code_length, bool prepend_header = true);
 
 // Compile a geometry shader to SPIR-V.
 bool CompileGeometryShader(SPIRVCodeVector* out_code, const char* source_code,
-                           size_t source_code_length);
+                           size_t source_code_length, bool prepend_header = true);
 
 // Compile a fragment shader to SPIR-V.
 bool CompileFragmentShader(SPIRVCodeVector* out_code, const char* source_code,
-                           size_t source_code_length);
+                           size_t source_code_length, bool prepend_header = true);
 
 // Compile a compute shader to SPIR-V.
 bool CompileComputeShader(SPIRVCodeVector* out_code, const char* source_code,
-                          size_t source_code_length);
+                          size_t source_code_length, bool prepend_header = true);
 
 }  // namespace ShaderCompiler
 }  // namespace Vulkan