Fix and deprecate TextUtils.join(Iterable<CharSequence>).

There seems to be only one caller of this signature, and even that is
in a deprecated method, so it should be safe to deprecate this.

The new implementation uses ICU for the format string and so removes
the need for a localized string, although it's still a hack and is
probably slower. It's added here since we may actually want to clean
it up later and use it for an improved simple list formatter.

Bug: 6823087
Change-Id: I2aa1af9b170e41da840d9d7bc663df06fb96d136