[XHR] No need to remember line number and URL on send() for inspector

XMLHttpRequest implementation has methods to set line number and URL of
send() method call to pass to
InspectorInstrumentation::didFinishXHRLoading(), but they are not used.
We can just remove this code. See below.

Since WebInspector.ConsoleMessage gets the corresponding request object
in its constructor using the requestId parameter and extracts the line
number and URL of send() method call, we don't need to remember and
pass them from the XMLHttpRequest class as far as we pass the request
identifier given on XMLHttpRequest::didFinishLoading() call to
InspectorInstrumentation::didFinishXHRLoading().

R=sigbjornf,eustas
BUG=none

Review URL: https://codereview.chromium.org/667393002

git-svn-id: svn://svn.chromium.org/blink/trunk@184163 bbb929c8-8fbe-4397-9dbb-9b2b20218538