Update Colvars to 2022-05-24 and copy of Lepton library

One bugfix for the Colvars library in the ABF method, and update of the copy
of the Lepton library as per the OpenMM repository.

List of relevant PR.

- 483 Update Lepton via patching procedure
  https://github.com/Colvars/colvars/pull/483 (@giacomofiorin)

- 482 Fix integer overflow in log_gradient_finite_diff and gradient_finite_diff
  https://github.com/Colvars/colvars/pull/482 (@HanatoK)

lib/colvars/colvarproxy_tcl.cpp

@@ -22,9 +22,7 @@
 
 colvarproxy_tcl::colvarproxy_tcl()
 {
-#ifdef COLVARS_TCL
   tcl_interp_ = NULL;
-#endif
 }