nmap: Add build flag '--without-nmap-update'

Without SVN installed, running nmap causes it to complain that 'libsvn_client-1.0.dylib' isn't loaded, which the nmap-update component depends on to connect to https://svn.nmap.org/updates to get NSE script updates.

Since it looks like https://svn.nmap.org/updates is only accessible to primary nmap developers at the moment, build nmap without nmap-update (rather than add SVN as a dependency).