gdb/copyright.py: Remove testsuite/gdb.base/step-line.{c,inp} special handling
    
    In the past, these files needed to be handled by hand, because
    the testcase was sensitive to the length of the header, which was
    potentially changing when new copyright years were added to
    the copyright header. Now that we simply maintain and update
    a range, the length of the copyright header should not change
    as a consequence of the update performed by this script, so
    special handling of those files is no longer necessary.
    
    gdb/ChangeLog:
    
            * copyright.py (BY_HAND): Remove gdb/testsuite/gdb.base/step-line.inp
            and gdb/testsuite/gdb.base/step-line.c.