Remove old version navigator content utils APIs

Old version navigator content utils APIs have been kept since r165458. Because
blink bots might ignore dependency with new content module. However, blink bots
is using updated content module which supports new navigator content utils APIs. Thus,
this cl removes the old navigator content utils APIs.

Review URL: https://codereview.chromium.org/232263003

git-svn-id: svn://svn.chromium.org/blink/trunk@171454 bbb929c8-8fbe-4397-9dbb-9b2b20218538