Fix post-mortem data after frame-marking changes

Post-mortem metadata generation broke as a result of
https://codereview.chromium.org/1696043002

BUG=

Review URL: https://codereview.chromium.org/1780933004

Cr-Commit-Position: refs/heads/master@{#34725}

tools/gen-postmortem-metadata.py

@@ -154,8 +154,6 @@ consts_misc = [
         'value': 'StandardFrameConstants::kContextOffset' },
     { 'name': 'off_fp_constant_pool',
         'value': 'StandardFrameConstants::kConstantPoolOffset' },
-    { 'name': 'off_fp_marker',
-        'value': 'StandardFrameConstants::kMarkerOffset' },
     { 'name': 'off_fp_function',
         'value': 'JavaScriptFrameConstants::kFunctionOffset' },
     { 'name': 'off_fp_args',