mesa/main: do not require float-texture filtering for es3

mesa/main: do not require float-texture filtering for es3

The OpenGL ES 3.0 specification, table 3.13 lists half-float textures as
filterable, but not float textures. So we shouldn't depend on
ARB_float_texture, which requires full filtering support for both.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>