adapter-idb/allDocs: simplify getMaxUpdateSeq() (#8762)

Author: alxndrsn

packages/node_modules/pouchdb-adapter-idb/src/allDocs.js

@@ -114,27 +114,13 @@ function idbAllDocs(opts, idb, callback) {
 
   /* istanbul ignore if */
   if (opts.update_seq) {
-    getMaxUpdateSeq(seqStore, function (e) {
-      if (e.target.result && e.target.result.length > 0) {
-        updateSeq = e.target.result[0];
-      }
-    });
-  }
-
-  function getMaxUpdateSeq(objectStore, onSuccess) {
-    function onCursor(e) {
+    // get max updateSeq
+    seqStore.openCursor(null, 'prev').onsuccess = e => {
       var cursor = e.target.result;
-      var maxKey = undefined;
       if (cursor && cursor.key) {
-        maxKey = cursor.key;
+        updateSeq = cursor.key;
       }
-      return onSuccess({
-        target: {
-          result: [maxKey]
-        }
-      });
-    }
-    objectStore.openCursor(null, 'prev').onsuccess = onCursor;
+    };
   }
 
   // if the user specifies include_docs=true, then we don't