Remove repeat and enforce-determinism options

These only functioned if a very narrow combination of conditions held:

- The result path does not yet exist (--check did not result in
  repeated builds), AND
- The result path is not available from any configured substituters, AND
- No remote builders that can build the path are available.

If any of these do not hold, a derivation would be built 0 or 1 times
regardless of the repeat option. Thus, remove it to avoid confusion.

src/libstore/daemon.cc

@@ -238,7 +238,6 @@ struct ClientSettings
                 }
                 else if (trusted
                     || name == settings.buildTimeout.name
-                    || name == settings.buildRepeat.name
                     || name == settings.maxSilentTime.name
                     || name == settings.pollInterval.name
                     || name == "connect-timeout"