Remove a bunch of unused configure tests, in particular cases where

Remove a bunch of unused configure tests, in particular cases where
* the result is not recorded anywhere
* the result is not used anywhere
* the result is only used in some places, whereas others have been getting away with it
* the result is used improperly

Also make command line options handling a little better (e.g., --disable-locale,
while redundant, should really still *dis*able).