[FFe] libopenscenegraph-dev Depends on libgl1-mesa-dev instead of libgles2-mesa-dev on armhf

This is a bugfix-only update.

The current version of libopenscenegraph-dev depends on libgl1-mesa-dev on all architectures, including on armhf, where it is built using libgles2-mesa-dev. Considering that only GLES is supported on Ubuntu armhf, and considering that the library wasn't built with libgl1-mesa-dev, the dependency should be changed to libgles2-mesa-dev.

Regarding the risk, the risk is low. This package previously did not build for armhf, and Utopic (currently) is the only release to have an armhf build of openscenegraph. Other packages that used this library likely either had an explicit dependency on libgles2-mesa-dev or used another package that pulled in libgles2-mesa-dev; if anything, some packages may fail to build after this change in the event those packages were built with OpenGL instead of OpenGL ES.