Uri: switch to std::string over fbstring take 2

Summary: Update tuple generated for hash/equal_to for `folly::Uri` to also use std::string

Reviewed By: Orvid

Differential Revision: D5199266

fbshipit-source-id: bcd619dae01ffbf82fbb5c8987b0e87103572452

folly/Uri-inl.h

@@ -29,14 +29,14 @@ namespace folly {
 namespace uri_detail {
 
 using UriTuple = std::tuple<
-    const fbstring&,
-    const fbstring&,
-    const fbstring&,
-    const fbstring&,
+    const std::string&,
+    const std::string&,
+    const std::string&,
+    const std::string&,
     uint16_t,
-    const fbstring&,
-    const fbstring&,
-    const fbstring&>;
+    const std::string&,
+    const std::string&,
+    const std::string&>;
 
 inline UriTuple as_tuple(const folly::Uri& k) {
   return UriTuple(