at this point, the cache is needed only to aggregate the modules,
not to "export" qtbase internals. the modules now have private caches
for "real" config data.

Change-Id: I4c70d220bbc054023710680545a04c171e238aff
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>