Revert of Verify EME needkey event property contentType (https://codereview.chromium.org/129793008/)

Reason for revert:
Caused compilation error on Android:

http://build.chromium.org/p/chromium.webkit/builders/Android%20Builder%20%28dbg%29/builds/23794/steps/compile/logs/stdio

Original issue's description:
> Verify EME needkey event property contentType
> 
> Now that the Chromium code has been updated to pass the MIME type
> of the media file, update the needkey test to verify the value.
> Also removes the old keyNeeded() interface which is no longer used.
> 
> BUG=224786
> TEST=EME content tests pass
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165805

TBR=xhwang@chromium.org,acolwell@chromium.org,abarth@chromium.org,jrummell@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=224786

Review URL: https://codereview.chromium.org/145273022

git-svn-id: svn://svn.chromium.org/blink/trunk@165807 bbb929c8-8fbe-4397-9dbb-9b2b20218538