flip_server: Remove unused http_message_constants.cc source file.
flip_server: Remove unused http_message_constants.cc source file.

I found this while looking at http_message_constants.cc and trying to
navigate to its header file in
https://code.google.com/p/chromium/codesearch#search/&q=package:%5E(chromium)$%20file:(/%7C%5E)net/tools/flip_server/http_message_constants%5C.h$&type=cs

BUG=None
R=mmenke@chromium.org,rch@chromium.org

Review URL: https://codereview.chromium.org/1353223002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#349801}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk