fix(ui): revert use mode:no-cors for fetch GET requests

responses for mode:no-cors requests have no body, which we need

ui/src/Common/Fetch.js

@@ -6,18 +6,7 @@ const CommonOptions = {
 };
 
 const FetchGet = async (uri, options) =>
-  await fetch(
-    uri,
-    merge(
-      {},
-      {
-        method: "GET",
-        mode: "no-cors"
-      },
-      CommonOptions,
-      options
-    )
-  );
+  await fetch(uri, merge({}, { method: "GET" }, CommonOptions, options));
 
 const FetchPost = async (uri, options) =>
   await fetch(uri, merge({}, { method: "POST" }, CommonOptions, options));

ui/src/Common/Fetch.test.js

@@ -18,7 +18,7 @@ describe("Fetch", () => {
   };
 
   const methodOptions = {
-    FetchGet: { method: "GET", mode: "no-cors" },
+    FetchGet: { method: "GET" },
     FetchPost: { method: "POST" },
     FetchDelete: { method: "DELETE" }
   };

ui/src/Components/SilenceModal/SilencePreview/index.test.js

@@ -89,7 +89,6 @@ describe("<SilencePreview />", () => {
       "./alerts.json?q=foo%3Dbar&q=%40alertmanager%3D~%5E%28amValue%29%24",
       {
         method: "GET",
-        mode: "no-cors",
         credentials: "include",
         redirect: "follow"
       }
@@ -108,7 +107,6 @@ describe("<SilencePreview />", () => {
       "./alerts.json?q=foo%3Dbar&q=%40alertmanager%3D~%5E%28am1%7Cam2%29%24",
       {
         method: "GET",
-        mode: "no-cors",
         credentials: "include",
         redirect: "follow"
       }