trim --prune: Look at FLAG_NO_SIDE_EFFECTS rather than FLAG_VERBOSE

The --prune option is documented precisely to prune calls with no side
effects, so that's the flag it should examine.

Previously, the trim --prune code was keying off of the VERBOSE
flag. This hasn't made a substantial difference in the past, (the
NO_SIDE_EFFECTS calls have historically all been VERBOSE as well). But
NO_SIDE_EFFECTS has the advantage that it can objectively determined,
so the set of calls that should have this flag should be
unambiguous. (Meanwhile, whether any particular call should be
classified as VERBOSE is inherently subjective.)
trim: Don't consider a SwapBuffers call has having no side effects

I can't justify why I ever added this code. I can only guess that I was
trying to get qapitrace to not show frame markers for frames that had
largely been trimmed.

Anyway, the code is wrong. SwapBuffers call obviously have significant
side effects. And the effect I was trying to achieve is already well
satisified by the change in 2f0d1a3244c8953a4468759ac466b80c4965d38f
that will trim a SwapBuffers call when --trim-spec=drawing is in
force.
trim: Greatly expand the list of calls considered to have no side effects

The list of calls added here with the NO_SIDE_EFFECTS flag was
obtained from the existing specs/glapi.py file, (all calls with
"sideeffects=False").

It's a bit unfortunate that we have this duplication of information in
the source tree, (two different lists of calls with no side
effects). But that duplication was already present before this
commit. This commit merely brings this list into sync with the other.
trim: Don't trim user-inserted debugging calls as having no side effect

While a call like glPushDebugGroup or glStringMarkerGREMEDY may
technically not effect the OpenGL state, users put these calls in
place specifically to be able to get more information out of tools
such as apitrace. So we definitely don't want to trim these calls out
when a user requests trimming or pruning calls with no side effects.