Remove ScriptPromiseResolver.

As ScriptPromiseResolverWithContext is widely used and having two similar
classes is confusing, this CL removes ScriptPromiseResolver.
Note: ScriptPromiseResolverWithContext will be renamed to ScriptPromiseResolver
in the future.

BUG=386479

Review URL: https://codereview.chromium.org/340293003

git-svn-id: svn://svn.chromium.org/blink/trunk@176589 bbb929c8-8fbe-4397-9dbb-9b2b20218538