tests/gl_basic: Remove usage of soon-to-be-killed api attribute
tests/gl_basic: Remove usage of soon-to-be-killed api attribute

Replace usage of the soon-to-be-killed WAFFLE_OPENGL_API attribute with
WAFFLE_CONTEXT_API.

Signed-off-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>

maurossi/waffle,dcbaker/waffle,waffle-gl/waffle,waffle-gl/waffle,waffle-gl/waffle,yinquan529/waffle-gl-waffle,fjhenigman/waffle,chadversary/waffle,yinquan529/waffle-gl-waffle,dcbaker/waffle,janesma/waffle,fjhenigman/waffle,maurossi/waffle,maurossi/waffle,fjhenigman/waffle,yinquan529/waffle-gl-waffle,waffle-gl/waffle,evelikov/waffle,chadversary/waffle,janesma/waffle,evelikov/waffle,evelikov/waffle,janesma/waffle,chadversary/waffle,dcbaker/waffle