anv: Drop stale comment in anv_cmd_buffer_emit_binding_table()

anv: Drop stale comment in anv_cmd_buffer_emit_binding_table()

When emitting the binding table for the fragment shader stage, we no
longer "walk all of the attachments, [inserting only] the color
attachments into the binding table". Instead, we iterate only over the
subpass's color attachments, which is the minimal possible iteration.

While killing the comment, also rename the variable 'attachments' to
'color_count', as it's no longer a count of all framebuffer attachments
but only the subpass's color attachment count.