Web MIDI API renaming: the last step of three step changes 

Remove old functions. Now there are no 'SysEx' and 'sysEx' strings
in Web MIDI implementation after this change.

Here are a series of changes on this renaming. 
1. https://codereview.chromium.org/208243014/
2. https://codereview.chromium.org/210003002/
3. this change

BUG=349538
TEST=LayoutTests/webmidi

Review URL: https://codereview.chromium.org/208423016

git-svn-id: svn://svn.chromium.org/blink/trunk@170062 bbb929c8-8fbe-4397-9dbb-9b2b20218538