terminal-util: don't issue "ESC c" sequence on reset, but only when erasing the screen

terminal-util: don't issue "ESC c" sequence on reset, but only when erasing the screen

ESC c is a (vaguely defined) "reset to initial state" ANSI sequence.
Many terminals clear the screen in this case, but that's a bit drastic I
think for most resets.

ESC c was added to the reset logic in
00bc83a275fa3ca8d90579fe9597d8b651d47332 (i.e. very recently), and I
don't think the effect was clear at that time.

Let's keep the ESC c in place however when we actually want to clear the
screen. Hence move it from reset_terminal_fd() into vt_disallocate().

Fixes: #33689