gsk: Use has_bgra in more places

gsk: Use has_bgra in more places

The glyph and icon libaries were also checking for GLES to
decide if data needs to be transformed from BGRA to RGBA.

Use the new has_bgra getter instead.

This will probably break on bigendian, because the
GL_BGRA + GL_UNSIGNED_BYTE combination is not equivalent
to the cairo format on bigendian, but this was already
broken for the gl format information that we get from
gdk_memory_format_gl_format.