WebView: fix docs for setAllow*AccessFromFileUrls

No change to behavior, only docs change.

The docs for setAllow(File|Universal)AccessFromFileUrls were previously
wrong. They implied that:

 * Default value is 'false' when SDK_INT > Jellybean
 * APIs were added in Jellybean (so they can't be called pre-Jellybean)
 * Therefore, setAllow*AccessFromFileUrls(false) is always a NOOP

Actually, WebView examines targetSdk, not SDK_INT. So apps should call
setAllow*AccessFromFileUrls(false) when targeting ICE_CREAM_SANDWICH_MR1
and below.

The docs previously had mixed use of ICE_CREAM_SANDWICH and
ICE_CREAM_SANDWICH_MR1. This corrects the docs to use the right one
(ICE_CREAM_SANDWICH_MR1).

Lastly, this fixes a minor grammar mistake (misplaced comma).

Test: make docs (manually verify)
Change-Id: I206dff54a8c342ae7b47bd40d69d0b01dbad3cc6