src: remove OnScopeLeaveImpl's move assignment overload

... as it's not valid implementation and also has not been used

PR-URL: #48732
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

src/util.h

@@ -577,12 +577,6 @@ struct OnScopeLeaveImpl {
     : fn_(std::move(other.fn_)), active_(other.active_) {
     other.active_ = false;
   }
-  OnScopeLeaveImpl& operator=(OnScopeLeaveImpl&& other) {
-    if (this == &other) return *this;
-    this->~OnScopeLeave();
-    new (this)OnScopeLeaveImpl(std::move(other));
-    return *this;
-  }
 };
 
 // Run a function when exiting the current scope. Used like this: