terminal: Clear line using escapes instead of SIGINT

Sending SIGINT can be destructive, for example if we interrupt the
loading of the shell init files (e.g. .bashrc) and clobber history
preservation settings. Follow the example of Kate and send a Ctrl-E
Ctrl-U to clear the prompt instead.

BUG: 279614
Signed-off-by: John Brooks <john@fastquake.com>