winsys-wgl: Don't include cogl.h
winsys-wgl: Don't include cogl.h

Since 248a76f5eac7e5ae4fb45208577f9a55360812a7 cogl.h can no longer be
included in internal source files so the WGL winsys was no longer
compiling.

Reviewed-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

djdeath/cogl,djdeath/cogl,djdeath/cogl