Searching: Always set the limit when searching.

The spec doesn't mention any default limit so different homeservers
might use different defaults, since we don't want Riot to behave
differently depending on the homeserver bite the bullet of sending an
additional 10 or so bytes when searching.

src/Searching.js

@@ -22,15 +22,11 @@ const SEARCH_LIMIT = 10;
 async function serverSideSearch(term, roomId = undefined, processResult = true) {
     const client = MatrixClientPeg.get();
 
-    let filter;
-    if (roomId !== undefined) {
-        // XXX: it's unintuitive that the filter for searching doesn't have
-        // the same shape as the v2 filter API :(
-        filter = {
-            rooms: [roomId],
-            limit: SEARCH_LIMIT,
-        };
-    }
+    const filter = {
+        limit: SEARCH_LIMIT,
+    };
+
+    if (roomId !== undefined) filter.rooms = [roomId];
 
     const body = {
         search_categories: {