Remove obsolete DONT_USE_FENCE_SYNC option

Unable to find any recent uses of DONT_USE_FENCE_SYNC
and EGL_KHR_fence_sync is a CDD required extension, so
device support must be present.

So remove this last config option from libgui, and then
also remove the dump methods that just return the library name.

Test: builds
Change-Id: I29362d6cb7ce9ef9f2338dcbf55814973abd6c3d