JetEvent: Fix gcc9 warnings.
In C++11, implicit declarations of copy and assignment are deprecated if the class has a user defined destructor or copy or assignment. gcc9 now warns about this by default. Adjust to avoid the warning.
In C++11, implicit declarations of copy and assignment are deprecated if the class has a user defined destructor or copy or assignment. gcc9 now warns about this by default. Adjust to avoid the warning.