Plugins: Refactor cleaning of call resource response headers (#67145)

First part of #66889 moving cleaning of call resource response headers 
within plugin management client.

pkg/api/plugin_resource.go

@@ -161,7 +161,6 @@ func (hs *HTTPServer) flushStream(stream callResourceClientResponseStream, w htt
 
 		// Expected that headers and status are only part of first stream
 		if processedStreams == 0 {
-			var hasContentType bool
 			for k, values := range resp.Headers {
 				// Convert the keys to the canonical format of MIME headers.
 				// This ensures that we can safely add/overwrite headers
@@ -169,15 +168,6 @@ func (hs *HTTPServer) flushStream(stream callResourceClientResponseStream, w htt
 				// and be sure they won't be present multiple times in the response.
 				k = textproto.CanonicalMIMEHeaderKey(k)
 
-				switch k {
-				case "Set-Cookie":
-					// Due to security reasons we don't want to forward
-					// cookies from a backend plugin to clients/browsers.
-					continue
-				case "Content-Type":
-					hasContentType = true
-				}
-
 				for _, v := range values {
 					// TODO: Figure out if we should use Set here instead
 					// nolint:gocritic
@@ -185,13 +175,6 @@ func (hs *HTTPServer) flushStream(stream callResourceClientResponseStream, w htt
 				}
 			}
 
-			// Make sure a content type always is returned in response
-			if !hasContentType && resp.Status != http.StatusNoContent {
-				w.Header().Set("Content-Type", "application/json")
-			}
-
-			proxyutil.SetProxyResponseHeaders(w.Header())
-
 			w.WriteHeader(resp.Status)
 		}