cogl: don't include cogl-vector.h twice in cogl.h
cogl: don't include cogl-vector.h twice in cogl.h

cogl-vector.h should only be included by cogl.h when
COGL_ENABLE_EXPERIMENTAL_API is defined. This removes the unguarded
duplicate include.

gcampax/cogl,Distrotech/cogl,djdeath/cogl-android,collects/cogl,spatulasnout/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,Distrotech/cogl,djdeath/cogl,spatulasnout/cogl,djdeath/cogl,gcampax/cogl,djdeath/cogl-android,collects/cogl,Distrotech/cogl,djdeath/cogl,gcampax/cogl