copies: delete now-unnecessary check for "a == b" before "a.descendant(b)"
Unnecessary since
879cbdde63df (revlog: do inclusive descendant
testing (API), 2018-06-21).
Differential Revision: https://phab.mercurial-scm.org/D3935
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.