fortran: Remove reference count update [PR108957]

fortran: Remove reference count update [PR108957]

Remove one reference count incrementation following the assignment of a
symbol pointer to a local variable.  Most symbol pointers are "weak" pointer
and don't need any reference count update when they are assigned, and it is
especially the case of local variables.

This fixes a memory leak with the testcase from the PR (not included).

	PR fortran/108957

gcc/fortran/ChangeLog:

	* gfortran.h (gfc_symbol): Add comment documenting reference counting.
	* parse.cc (parse_interface): Remove reference count incrementation.