routing: remove dysfunctional route to pullrequest copy_update Commit d42d7b2a3b2fec0cbf8380a22f4dd96fc836f5c5 refactored the pullrequest update functionality, making the route 'pullrequest_copy_update' redundant, but forgot to remove that route.

[tox]
envlist = py{26,27}-{pytest,nose}

[testenv]
setenv =
    PYTHONHASHSEED = 0
deps =
    nose: nose
    pytest: pytest
commands =
    nose: nosetests {posargs}
    pytest: py.test {posargs}