[Piglit] Deleting ~20% of glean/no more directory spam

[Kenneth Graunke]

This series deletes roughly 20% of Piglit's import of Glean:

1. Benchmarking 

   Piglit is a not a benchmarking suite---it's a test suite.  It has no
   infrastructure for even running these tests, so there's no need to
   keep them around.

2. Image output code

   Jose nuked most of this, removing the dependence on libtiff, libpng,
   and zlib.  There was a bit more dead code left, though.

3. Result "databases"

   One major annoyance when working with Glean is that it creates
   piles of files and directories, and in order to run any test, you
   need to tell it where to dump all of that.  And remember to delete
   it when you're done debugging a test failure.

   Having Glean create results files makes perfect sense for a standalone
   test suite---but in Piglit, we already store results in piglit-run.py's
   JSON output and create nice reports with piglit-summary-html.py.  It's
   unnecessary.

   Patch 13 removes support for comparing results databases.
   Patch 15 removes support for creating them altogether, and also removes
   the '-r' option since the path argument isn't necessary, and running
   is the only remaining action other than --listtests.

Now that Piglit's import of Glean is beginning to diverge from Glean proper,
my hope is that someday people will port over various tests to the native
Piglit framework, then delete the equivalent Glean code.  A bit more work
is necessary, like adding multi-visual support to Piglit, but we want to do
that anyway.