test: clean up struct cmd strings
test: clean up struct cmd strings

There is no good reason to have the strings be arrays. The compiler
would probably warn if the strings got too big, but it might not
warn if there the only thing that would fit was the trailing '\0'.

    char foo[8] = "abcdefgh";  /* might not be '\0' terminated */

bradparks/tmux-MacOSX-pasteboard,ChrisJohnsen/tmux-MacOSX-pasteboard,tjt263/tmux-MacOSX-pasteboard,lembacon/tmux-MacOSX-pasteboard