Replace getaddrinfo resolver with trust-dns-resolver

src/client.rs

@@ -281,13 +281,6 @@ impl ClientBuilder {
         self
     }
 
-    /// Set the number of threads to use for DNS
-    ///
-    /// Default is 4
-    pub fn dns_threads(self, threads: usize) -> ClientBuilder {
-        self.with_inner(|inner| inner.dns_threads(threads))
-    }
-
     fn with_inner<F>(mut self, func: F) -> ClientBuilder
     where
         F: FnOnce(async_impl::ClientBuilder) -> async_impl::ClientBuilder,