[Development] Apparently dead code: GPU_BLACKLIST and friends

[Edward Welbourne]

Hi all,

I notice that QTest includes support, in [0], alongside its BLACKLIST
files for problematic tests, for a GPU_BLACKLIST file; there are,
however, no GPU_BLACKLIST files anywhere in our source tree (in any
currently live branch, from 5.6 to dev).  There's a whole complex
QTEST_ADD_GPU_BLACKLIST_SUPPORT macro set-up for a hook function named
gpu_features() to control this; unless that's activated *and* a
GPU_BLACKLIST file is found, the whole GPU blacklisting feature does
nothing.

* [0] qtbase/src/testlib/qtestblacklist.cpp

Inevitably, I'm contemplating a featurectomy.  Laszlo, who introduced
this for some fragile embedded systems in 2015, doesn't believe it's in
use, I don't see any evidence that it's documented anywhere (so I don't
expect anyone to be using it outside Qt itself *and* I can only work out
how it's supposed to work by reading its code), so I'm hoping no-one
will object to this going, perhaps even as soon as 5.12.

So, if you're using GPU_BLACKLIST files, please speak up now (or forever
hold your peace); and, if you can think of a good reason why this can't
be removed from 5.12 - assuming I get round to it before feature freeze
- please also speak up,

	Eddy.