make gdkquartz-cocoa-access.h usable again

there is no need to include gdkquartz.h there, which was making it impossible to include this header file without also adding gdk/ as an include directory when compiling. This patch moves the include to the only location where it is actually needed.

More details can be found here: !4303, https://github.com/jralls/gtk-osx-build/pull/84