* gnu/packages/python.scm (python-3.6): Rename to ...
(python-3.7): ... this. Update to 3.7.0.
[arguments]: Remove phase 'patch-timestamp-for-pyc-files' and related code.
Add phases to unset SOURCE_DATE_EPOCH during the check phase.
(python-3): Is now PYTHON-3.7.
* guix/build/python-build-system.scm (enable-bytecode-determinism): Don't set
DETERMINISTIC_BUILD.