Detemplateify intToHexString

The routine of intToHexString is mostly common between all the
various implementations, the only difference is in selecting a
reasonable default size for the type.  This commit moves to a common
method, so the templates don't get created for each and every
instantiation of intToHexString, and simplifies our code.

This saves a trivial amount (428 bytes) of compressed binary size.

Tested: Unit tests passing, and have good coverage of this.

Memory resources return the values as were there previously.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I6945a81a5e03c7a64d6a2a0629b24db941271930