Remove scm.SVN from depot_tools

This code is no longer imported by anything.

BUG=475320

Change-Id: Ib03f1185c3d90e271f4ee4bff6ad0184454facb8
Reviewed-on: https://chromium-review.googlesource.com/422463Reviewed-by: Katie Thomas <katthomas@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

tests/scm_unittest.py

@@ -60,7 +60,6 @@ class RootTestCase(BaseSCMTestCase):
         'os',
         're',
         'subprocess2',
-        'SVN',
         'sys',
         'tempfile',
         'time',