RFR(XS): 8226286 Remove unused method java.lang.Integer::formatUnsignedInt

[Tagir Valeev]

Hello!

Please review:
https://bugs.openjdk.java.net/browse/JDK-8226286
http://cr.openjdk.java.net/~tvaleev/webrev/8226286/r1/

I left dangling javadoc in-place in the same way as it's done in
java.lang.Long.

Also I removed redundant reassignment of parameter like s =
Objects.requireNonNull(s).

By the way I noticed that remaining methods formatUnsignedInt
and formatUnsignedIntUTF16 always accept offset = 0. Probably it would be
good to inline offset parameter?

With best regards,
Tagir Valeev