tests/test-addremove.t

hgdemandimport: disable on Python 3.5

The demand importer functionality isn't working at all on Python 3.5.
I'm not sure what's wrong.

Since it isn't working, let's disable it completely.

```
$ HGRCPATH= hyperfine -w 1 -r 50 -- "~/.pyenv/versions/3.5.9/bin/python ./hg version" \
  "HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version"
Benchmark #1: ~/.pyenv/versions/3.5.9/bin/python ./hg version
  Time (mean ± σ):     163.7 ms ±   2.2 ms    [User: 148.5 ms, System: 15.7 ms]
  Range (min … max):   161.0 ms … 170.2 ms    50 runs

Benchmark #2: HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version
  Time (mean ± σ):     164.3 ms ±   1.4 ms    [User: 148.2 ms, System: 16.6 ms]
  Range (min … max):   161.4 ms … 169.8 ms    50 runs
```

Differential Revision: https://phab.mercurial-scm.org/D7953

  $ hg init rep
  $ cd rep
  $ mkdir dir
  $ touch foo dir/bar
  $ hg -v addremove
  adding dir/bar
  adding foo
  $ hg -v commit -m "add 1"
  committing files:
  dir/bar
  foo
  committing manifest
  committing changelog
  committed changeset 0:6f7f953567a2
  $ cd dir/
  $ touch ../foo_2 bar_2
  $ hg -v addremove
  adding dir/bar_2
  adding foo_2
  $ hg -v commit -m "add 2"
  committing files:
  dir/bar_2
  foo_2
  committing manifest
  committing changelog
  committed changeset 1:e65414bf35c5
  $ cd ..
  $ hg forget foo
  $ hg -v addremove
  adding foo
  $ hg forget foo

  $ hg -v addremove nonexistent
  nonexistent: $ENOENT$
  [1]

  $ cd ..

  $ hg init subdir
  $ cd subdir
  $ mkdir dir
  $ cd dir
  $ touch a.py
  $ hg addremove 'glob:*.py'
  adding a.py
  $ hg forget a.py
  $ hg addremove -I 'glob:*.py'
  adding a.py
  $ hg forget a.py
  $ hg addremove
  adding dir/a.py
  $ cd ..

  $ hg init sim
  $ cd sim
  $ echo a > a
  $ echo a >> a
  $ echo a >> a
  $ echo c > c
  $ hg commit -Ama
  adding a
  adding c
  $ mv a b
  $ rm c
  $ echo d > d
  $ hg addremove -n -s 50 # issue 1696
  removing a
  adding b
  removing c
  adding d
  recording removal of a as rename to b (100% similar)
  $ hg addremove -ns 50 --color debug
  [ui.addremove.removed ui.status|removing a]
  [ui.addremove.added ui.status|adding b]
  [ui.addremove.removed ui.status|removing c]
  [ui.addremove.added ui.status|adding d]
  [ ui.status|recording removal of a as rename to b (100% similar)]
  $ hg addremove -s 50
  removing a
  adding b
  removing c
  adding d
  recording removal of a as rename to b (100% similar)
  $ hg commit -mb
  $ cp b c
  $ hg forget b
  $ hg addremove -s 50
  adding b
  adding c

  $ rm c

  $ hg ci -A -m "c" nonexistent
  nonexistent: $ENOENT$
  abort: failed to mark all new/missing files as added/removed
  [255]

  $ hg st
  ! c
  $ cd ..