DevTools: Remove breakpoint locations once removing breakpoint from debugger is finished.

Breakpoint might have been resolved during removing, so clean up.

R=sergeyv

Review URL: https://codereview.chromium.org/350383003

git-svn-id: svn://svn.chromium.org/blink/trunk@177743 bbb929c8-8fbe-4397-9dbb-9b2b20218538