scons: Don't check for Python 2
scons: Don't check for Python 2

The build system will now refuse to build gem5 if Python 2.x is
detected. Remove Python 2 specific python-config variants from the
list of candidates we try.

Change-Id: Id59be4a2969ce180848e5df02afdfb4a5b8125c1
Signed-off-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36535
Reviewed-by: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5