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/iosource/IOSource.h

@@ -87,9 +87,3 @@ private:
 };
 
 } // namespace zeek::iosource
-
-namespace iosource {
-
-using IOSource [[deprecated("Remove in v4.1. Use zeek::iosource::IOSource.")]] = zeek::iosource::IOSource;
-
-} // namespace iosource