Fix setting groups visibility

Change I60c50a6c4 introduced a broken way of setting the visibility.

This commit fixes it as setting false in a string equals true in
javascript.

The check was also unneeded as it will be false by default (if not set).

Bug: Issue 10587
Change-Id: Ife40780f162d4eb5e3f75f4a6ed65f01aa7dc0e4
(cherry picked from commit b7b5cf0067ffa6a4c54c7791e4ee67b5146f9214)
diff --git a/polygerrit-ui/app/elements/admin/gr-group/gr-group.js b/polygerrit-ui/app/elements/admin/gr-group/gr-group.js
index a5f8757..3067bf6 100644
--- a/polygerrit-ui/app/elements/admin/gr-group/gr-group.js
+++ b/polygerrit-ui/app/elements/admin/gr-group/gr-group.js
@@ -162,13 +162,10 @@
     },
 
     _handleSaveOptions() {
-      let options;
-      // The value is in string so we have to convert it to a boolean.
-      if (this._groupConfig.options.visible_to_all) {
-        options = {visible_to_all: true};
-      } else if (!this._groupConfig.options.visible_to_all) {
-        options = {visible_to_all: false};
-      }
+      const visible = this._groupConfig.options.visible_to_all;
+
+      const options = {visible_to_all: visible};
+
       return this.$.restAPI.saveGroupOptions(this.groupId,
           options).then(config => {
             this._options = false;