presubmit_unittest: Fix pylint errors.
presubmit_unittest: Fix pylint errors.

The recent pylint 1.3.1 and 1.4.0 upgrades have caused some new errors
to be reported for presubmit_unittest:

* presubmit_support.InputApi.AffectedFiles() expectes a parameter called
  |include_deletes|, not |include_deleted|.

* The mock AffectedFiles() implementation in
  CannedChecksUnittest.testCannedCheckChangeHasNoTabs() had its
  signature updated to match the one in presubmit_support.InputApi,
  otherwise pylint would (erroneously) consider that this mock
  implementation was used in all other AffectedFiles() invocations in
  CannedChecksUnittest and complain that some parameters were missing.
  It makes more sense to do this than disable the check and miss real
  problems in the future.

R=maruel@chromium.org, iannucci@chromium.org, pgervais@chromium.org
BUG=443232

Review URL: https://codereview.chromium.org/802403003

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@293468 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

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