state provider: drop confirm-query when going back over initial history

state provider: drop confirm-query when going back over initial history

eslint complains about the window.confirm call, and neither I nor
some other colleagues here did see that dialogue ever in practice.

The confirm here does not adds any real value, as all other back
navigation are unprotected, but have similar potential in loosing
state.

One can always navigate forward via their user agent and for console
(noVNC, xterm.js) we have now a separate check.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>