mesa: Update todo regarding StencilOp and StencilOpSeparate.

mesa: Update todo regarding StencilOp and StencilOpSeparate.

OpenGL 2.0 function StencilOp() is in part internally implemented via
StencilOpSeparate(). This change happened some time ago, however the
accompanying doxygen todo comment was not accordingly updated.

Replace the outdated portion of this doxygen todo comment, leaving the
remainder unchanged.

Also better respect the 80 character suggested line length in this file.

v2: Fully remove comment, following code review by t_arceri@yahoo.com.au

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>