mesa: Remove support for GL_EXT_blend_logic_op

mesa: Remove support for GL_EXT_blend_logic_op

Support is removed for four reasons:

1. The implementation was broken with respect to separate blend
equations.  The GL_EXT_blend_equation_separate spec says:

    "If EXT_blend_logic_op and EXT_blend_equation_separate are both
    supported, the logic op blend equation should be supported separately
    for RGB and alpha as with the other blend equation modes."

But Mesa's implementation of GL_LOGIC_OP specifically forbids this.

2. No hardware supported by Mesa can support separate blend equations
involving GL_LOGIC_OP.

3. No applications could be found that use this extension.

4. No other Linux OpenGL drivers support this extension.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
Cc: Brian Paul <brianp@vmware.com>