do not expose headers_mut via HttpMessage

src/client/response.rs

@@ -24,10 +24,6 @@ impl HttpMessage for ClientResponse {
         &self.head.headers
     }
 
-    fn headers_mut(&mut self) -> &mut HeaderMap {
-        &mut self.head.headers
-    }
-
     fn extensions(&self) -> Ref<Extensions> {
         self.head.extensions()
     }

src/httpmessage.rs

@@ -32,9 +32,6 @@ pub trait HttpMessage: Sized {
     /// Read the message headers.
     fn headers(&self) -> &HeaderMap;
 
-    /// Mutable reference to the message's headers.
-    fn headers_mut(&mut self) -> &mut HeaderMap;
-
     /// Message payload stream
     fn take_payload(&mut self) -> Payload<Self::Stream>;
 
@@ -280,11 +277,6 @@ where
         (**self).headers()
     }
 
-    /// Mutable reference to the message's headers.
-    fn headers_mut(&mut self) -> &mut HeaderMap {
-        (**self).headers_mut()
-    }
-
     /// Message payload stream
     fn take_payload(&mut self) -> Payload<Self::Stream> {
         (**self).take_payload()

src/request.rs

@@ -22,11 +22,6 @@ impl<P> HttpMessage for Request<P> {
         &self.head().headers
     }
 
-    #[inline]
-    fn headers_mut(&mut self) -> &mut HeaderMap {
-        &mut self.head_mut().headers
-    }
-
     /// Request extensions
     #[inline]
     fn extensions(&self) -> Ref<Extensions> {
@@ -107,6 +102,11 @@ impl<P> Request<P> {
         &mut *self.head
     }
 
+    /// Mutable reference to the message's headers.
+    fn headers_mut(&mut self) -> &mut HeaderMap {
+        &mut self.head_mut().headers
+    }
+
     /// Request's uri.
     #[inline]
     pub fn uri(&self) -> &Uri {