Emulator: Replace ro.kernel.qemu.gles with qemu.gles

ro.kernel.qemu.gles is passed in by emulator and is read only;
the actual gles version can only be decided at egl library
loading time, and qemu.gles value will be set there and be
queried here.

bug: 27273457
Change-Id: I5ba228a2fa6649786dc87da09367d368e9e6d1e8