python3-scons{-native}: upgrade 3.1.1 -> 3.1.2

python3-scons{-native}: upgrade 3.1.1 -> 3.1.2

THis release is a mix of improvements and fixes:
https://github.com/SCons/scons/blob/3.1.2/src/RELEASE.txt

* Changed to inherit pypi rather than relying on SOURCEFORGE_MIRROR.
* Add SRC_URI for LICENSE file (not included in pypi tarball).
* Make it more obvious that RDEPENDS are for class-target and
  drop empty RDEPENDS from -native
* python3-scons-native now DEPENDS on python3-setuptools-native

* Tested with core-image-base + packagegroup-core-buildessential
  with "scons" oe-selftest via testimage.
* Tested build of "serf" (which uses python3-scons-native via the
  scons.bbclass).

License-Update: Added "MIT License" text, updated copyright years

Signed-off-by: Tim Orling <timothy.t.orling@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>