Roll script: Update after SVN support was dropped from depot tools

After https://codereview.chromium.org/2404413002 PyLint started
failing for our roll script. This fixes that.

BUG=webrtc:6544
TBR=phoglund@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2425923002
Cr-Commit-Position: refs/heads/master@{#14654}

tools/autoroller/roll_chromium_revision.py

@@ -56,7 +56,6 @@ def ParseDepsDict(deps_content):
   local_scope = {}
   var = GClientKeywords.VarImpl({}, local_scope)
   global_scope = {
-    'File': GClientKeywords.FileImpl,
     'From': GClientKeywords.FromImpl,
     'Var': var.Lookup,
     'deps_os': {},