cogl: Remove _COGL_GET_CONTEXT usages
There are only 3 usages lefts:
cogl_get_proc_addressCoglRenderer.update_all_outputs_cogl_debug_dump_pipelines_dot_file
The first two are very annoying to untangle so I am leaving to someone else & the last one could be made to take a CoglContext...
Edited by Bilal Elmoussaoui