Use caching for SInteger objects like in Java

Caching code is directly inspired by OpenJDK's Integer class.
Also simplified simple new object methods in universe and removed non-sense comments.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Revert "Use caching for SInteger objects like in Java"

This reverts commit 9cc57cf1171833ece54d8ca76a045a41729c8b82.

On the current benchmarks, this change has a mostly negative impact on performance, ca. 5-20% slowdowns on some, no change on most others.

Signed-off-by: Stefan Marr <git@stefan-marr.de>