changectx: extract explicit computechangesetfilesremoved method from context
Right now, the logic around changeset centric removed files data are buried into
the "changectx" code. We extract this code in a dedicated method (in the scmutil
module) for clarity. This clarity will help to explicitly compute and caches
these data in the future.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..