scons: Don't explicitly list include dependencies for the cxx config.
scons: Don't explicitly list include dependencies for the cxx config.

SCons will scan c/c++ files for include dependencies itself, there's no
need to list them explicitly.

Change-Id: I295c22e52e38c53ab7705193f2fe2c98227ea70d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49403
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Yu-hsin Wang <6fe4a9bb86bd1d25c6bb6664bd84f1b6720c0b37@google.com>

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