GPU: Remove prototype without implementation.

`GPUShaderInterface(const ShaderCreateInfo&)` is defined but its
implementation has been removed.

source/blender/gpu/intern/gpu_shader_interface.hh

@@ -68,7 +68,6 @@ class ShaderInterface {
 
  public:
   ShaderInterface();
-  ShaderInterface(const shader::ShaderCreateInfo &info);
   virtual ~ShaderInterface();
 
   void debug_print();