egl: Remove old tuna BGRA vs RGBA workaround.

Some time before kitkat, a workaround was put in place to keep tuna
working with obsolete PowerVR GPU drivers. The tuna product was dropped
in AOSP for kitkat, but the workaround remained.

There are still a number of devices shipping with OMAP4 processors, and
this workaround continues to be applied on those products even when it
is not required. The effect is that virtual display CTS will fail on
those devices.