Remove all of the random single-file deprecations

These are the changes that don't require a ton of changes to other files outside
of the original removal.

src/threading/formatters/JSON.h

@@ -45,9 +45,3 @@ private:
 };
 
 } // namespace zeek::threading::formatter
-
-namespace threading::formatter {
-
-using JSON [[deprecated("Remove in v4.1. Use zeek::threading::formatter::JSON.")]] = zeek::threading::formatter::JSON;
-
-} // namespace threading::formatter