rebase: stop clearing on-disk mergestate when running in memory
In-memory merge no longer uses on-disk mergestate since
19590b126764
(merge: use in-memory mergestate when using in-memory context,
2020-09-15). This patch removes the clearing from two places in the
in-memory rebase code. I've verified that the one with a TODO was
indeed fixed by the aforementioned commit. The other instance doesn't
seem to have any test coverage, but I'm pretty confident it's also
safe to remove.
Differential Revision: https://phab.mercurial-scm.org/D9057
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3