Completes the CWX type-ahead loop: with send-on-type the keyer-panel CW text
already streams each typed char to the radio's CWX buffer (which keys in order,
so you can keep typing while it sends); this adds the matching un-send. Route
wkBackspace to FlexBackspaceCW -> cwx erase N, so backspacing a mistyped char in
send-on-type removes it from the buffer before the radio keys it.
rouggy
3cef885934