Remove cogl-1.0 vs cogl-2.0 vs cogl experimental API split

Mutter (and libmutter users) are the only users of this version of
cogl, and will more or less only use the cogl-1.0, cogl-2.0 and cogl
experimental API variants, and having the possibility of having
different API versions of the same API depending on what file includes
it is error prone and confusing. Lets just remove the possibility of
having different versions of the same API.

https://bugzilla.gnome.org/show_bug.cgi?id=768977

cogl/cogl/cogl-pipeline-layer-state.h

@@ -42,8 +42,6 @@
 
 COGL_BEGIN_DECLS
 
-#ifdef COGL_ENABLE_EXPERIMENTAL_API
-
 /**
  * CoglPipelineFilter:
  * @COGL_PIPELINE_FILTER_NEAREST: Measuring in manhatten distance from the,
@@ -613,8 +611,6 @@ cogl_pipeline_add_layer_snippet (CoglPipeline *pipeline,
                                  int layer,
                                  CoglSnippet *snippet);
 
-#endif /* COGL_ENABLE_EXPERIMENTAL_API */
-
 COGL_END_DECLS
 
 #endif /* __COGL_PIPELINE_LAYER_STATE_H__ */