Remove unnecassary parameter "sampleRate" for loadAudioResource().

Parameter "sampleRate" is not required for loadAudioResource().
There is FIXME in AudioBus.cpp in blink
FIXME: the sampleRate parameter is ignored. It should be removed from the API.

It will be consist of 3 steps. 
1. Removing "sampleRate" in chrome which is called by blink. (included deprecated method) 
https://codereview.chromium.org/195043002/ 

2. Removing "sampleRate" in blink. 
https://codereview.chromium.org/194753005/ 

3. Removing deprecated method from #1 

BUG=351284

Review URL: https://codereview.chromium.org/194753005

git-svn-id: svn://svn.chromium.org/blink/trunk@169188 bbb929c8-8fbe-4397-9dbb-9b2b20218538