Creating preferences.php is a waste of time

The get_preference() function is called a number of
times in tiki-setup before it get's to the point where
it creates the preferences.php "cache" file.

However, the first time get_preference() queries the db
and caches (in memory) the whole preferences table and
uses it for future lookups, that means that after the
first get_preference it's all in memory anyway.

So ... what is the point of creating the
preferences.php file? ... it doesn't stop any database
queries, add's the overhead of creating and reading it,
and breaks things in the cluster world.

This explains why performance is better when you take
that bit of code out!

So ... much better patch attached, just removal of code!