Add a default .subversion/servers configuration file that disables storage of passwords in plain text so you don't get prompted everytime.
Remove unneeded `unlink` of subversion servers file

The `unlink`s that we use in provision are there to help current VVV instances accept the new `cp` of config files rather than the old `ln` method. Any new files added don't need to be unlinked first.

See #200
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