remove Engine::filter_exists

It's not very practical and probably doesn't do what you expected,
anyways.

src/engine.rs

@@ -154,22 +154,6 @@ impl Engine {
         self.blocker.get_csp_directives(request)
     }
 
-    /// Check if a given filter has been previously added to this `Engine`.
-    ///
-    /// Note that only network filters are currently supported by this method.
-    pub fn filter_exists(&self, filter: &str) -> bool {
-        use crate::filters::network::NetworkFilter;
-        let filter_parsed = NetworkFilter::parse(filter, false, Default::default());
-        match filter_parsed.map(|f| self.blocker.filter_exists(&f)) {
-            Ok(exists) => exists,
-            Err(_e) => {
-                #[cfg(test)]
-                eprintln!("Encountered unparseable filter when checking for filter existence: {:?}", _e);
-                false
-            }
-        }
-    }
-
     /// Sets this engine's tags to be _only_ the ones provided in `tags`.
     ///
     /// Tags can be used to cheaply enable or disable network rules with a corresponding `$tag`

tests/legacy_harness.rs

@@ -686,15 +686,13 @@ mod legacy_misc_tests {
         let mut engine2 = Engine::new(false);
         engine2.deserialize(&serialized).unwrap();
 
-        assert!(engine.filter_exists("||googlesyndication.com$third-party"));
-        assert!(engine2.filter_exists("||googlesyndication.com$third-party"));
-        assert!(!engine.filter_exists("||googleayndication.com$third-party"));
-        assert!(!engine2.filter_exists("||googleayndication.com$third-party"));
-
-        assert!(engine.filter_exists("@@||googlesyndication.ca"));
-        assert!(engine2.filter_exists("@@||googlesyndication.ca"));
-        assert!(!engine.filter_exists("googlesyndication.ca"));
-        assert!(!engine2.filter_exists("googlesyndication.ca"));
+        assert!(engine.check_network_request(&Request::new("https://googlesyndication.com/script.js", "https://example.com", "script").unwrap()).matched);
+        assert!(engine2.check_network_request(&Request::new("https://googlesyndication.com/script.js", "https://example.com", "script").unwrap()).matched);
+        assert!(!engine.check_network_request(&Request::new("https://googleayndication.com/script.js", "https://example.com", "script").unwrap()).matched);
+        assert!(!engine2.check_network_request(&Request::new("https://googleayndication.com/script.js", "https://example.com", "script").unwrap()).matched);
+
+        assert!(!engine.check_network_request(&Request::new("https://googlesyndication.ca/script.js", "https://example.com", "script").unwrap()).matched);
+        assert!(!engine2.check_network_request(&Request::new("https://googlesyndication.ca/script.js", "https://example.com", "script").unwrap()).matched);
     }
 
     #[test]