Remove glext.h.
Remove glext.h.

It's part of ogl not ocl.

Signed-off-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@linux.intel.com>

ignatenkobrain/beignet,wdv4758h/beignet,ignatenkobrain/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,wdv4758h/beignet,ignatenkobrain/beignet,wdv4758h/beignet,wdv4758h/beignet,ignatenkobrain/beignet,zhenyw/beignet,ignatenkobrain/beignet,wdv4758h/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet