check-py3-compat: drop support for Python 2 We no longer support Python 2 so we can drop support for linting code for Python 2 support. This gets rid of the check for `from __future__`, enabling us to delete those imports. Differential Revision: https://phab.mercurial-scm.org/D12251

pycompat: remove large Python 2 block We no longer support Python 2. So we can delete its compatibility code and remove the conditional and dedent the Python 3 code. In order to make the linter happy, we had to inline imports in the stanza at the top of the file. Differential Revision: https://phab.mercurial-scm.org/D12250

py3: use pickle directly pycompat.pickle abstracted over the different pickle modules in Python 2 and 3. Now that we're Python 3 only, it is safe to use the `pickle` module directly. So this commit does that. As part of this we remove the rules from check-code.py that were forbidden direct pickle module use. We retain the `util.pickle` symbol for backwards compatibility, just in case some extensions were using it. Differential Revision: https://phab.mercurial-scm.org/D12249

pycompat: remove first not ispy3 block We now require Python 3. So we can remove the first block supporting Python 2. Differential Revision: https://phab.mercurial-scm.org/D12247

import-checker: assume absolute and use modern import checker Since we require Python 3 now, we can assume we always use absolute imports and the modern import checker should be used. Differential Revision: https://phab.mercurial-scm.org/D12246

tests: unconditionalize some imports Now that we require Python 3 we can simplify these imports. Differential Revision: https://phab.mercurial-scm.org/D12245

tests: remove last references to PYTHON3 This removes the last references to PYTHON3. Differential Revision: https://phab.mercurial-scm.org/D12244