perf build: Remove explicit reference to python 2.x devel files

If the libpython feature test (tools/build/feature/test-libpython.c)
fails, then the python-devel is missing, it doesn't mattere if it is for
python2 or 3, remove that explicit 2.x reference.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>