merge: remove direct rustmod reference
We shouldn't rely on this member being present in `dirstate.py`, this creates
unnecessary coupling.
This also can trigger certain issues in edge-cases where the policy is changed
at runtime or multiple Python environments fight, which is an added bonus.
Differential Revision: https://phab.mercurial-scm.org/D12217
$ hg init
$ echo "added file1" > file1
$ echo "added file2" > file2
$ hg add file1 file2
$ hg commit -m "added file1 and file2"
$ echo "changed file1" >> file1
$ hg commit -m "changed file1"
$ hg -q log
1:08a16e8e4408
0:d29c767a4b52
$ hg id
08a16e8e4408 tip
$ hg update -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg id
d29c767a4b52
$ echo "changed file1" >> file1
$ hg id
d29c767a4b52+
$ hg revert --all
reverting file1
$ hg diff
$ hg status
? file1.orig
$ hg id
d29c767a4b52
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg update -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "changed file1" >> file1
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg revert --all
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg revert -r tip --all
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg update -C
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip