Remove WebInspector.HeapSnapshotArraySlice

Uin32Array already has subarray method that returns a new view for the same array buffer.

BUG=None
R=alph@chromium.org

Review URL: https://codereview.chromium.org/204563002

git-svn-id: svn://svn.chromium.org/blink/trunk@169554 bbb929c8-8fbe-4397-9dbb-9b2b20218538