Delete useless code in ArcanistBaseWorkflow

Test Plan: This diff.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4601
Mark deleted paths as removed in committing

Test Plan: Deleted file in Git, ran `arc diff`, confirmed the question, saw the file as deleted.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4603
Fix `arc diff --no-ansi`

Summary: Currently, we get an exception on empty %Ls for `arc diff --no-ansi` or similar (see P698).

Test Plan: Ran `arc diff --no-ansi`.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4624
Don't bail on no effect exception

Summary: The main reason for this is to not exit with 1 when no paths are lintable (which is more success than failure).

Test Plan:
Returned empty array from `buildLinters()`, then:

  $ arc lint
  $ echo $? # 0

Reviewers: epriestley

Reviewed By: epriestley

CC: wez, aran, Korvin

Differential Revision: https://secure.phabricator.com/D4625
Cache results of repository linters

Summary:
The cache key is repository base revision and hash of all modified files.
It isn't perfect in SVN where every file might have a different revision.
It's also suboptimal as just committing or amending changes the cache key even if the files contents weren't modified.
We can improve it later, perhaps by using previous revision and files modified since it.

Test Plan:
Changed granularity of XHPAST linter to repository.
Linted the same repo twice, verified that it was read from cache the second file.
Changed a single file, verified that all files were re-linted.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4608
Revert "Delete useless code in ArcanistBaseWorkflow"

This reverts commit rARC501e2b7.
We call this method from FB workflow.
I'll commit it again in two weeks.
Merge branch 'master' of http://github.com/facebook/arcanist