Address cppcheck complaints

src/activities/home/FileBrowserActivity.cpp

@@ -256,7 +256,7 @@ void FileBrowserActivity::loop() {
 
 std::string getFileName(std::string filename) {
   if (filename.back() == '/') {
-    filename = filename.substr(0, filename.length() - 1);
+    filename.pop_back();
     if (!UITheme::getInstance().getTheme().showsFileIcons()) {
       return "[" + filename + "]";
     }