The ifdef gave an impression of the code path being hit only when
texture-backed widgets are present and OpenGL-based compositing is
active. This is false. Asserting on having a context current is
wrong (as shown by autotests on the 5.6 branch).

Change-Id: I2539f0aac75b26597f49f63edcd9580428be79b7
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>