Bug#1079886: backspace/^H isn't interpreted properly anymore

[VA]

Package: libvte-2.91-0:amd64
Version: 0.77.91-2

I don't know what changed, but suddenly many things bound to 
backspace/ctrl-h don't work properly.
I will be comparing 0.76* to 0.77.91-2.

## Example in zsh

To reproduce:

- start zsh
- run: bindkey "$termcap[kb]" backward-kill-word
- press a few characters to have something in the buffer to delete
- then…

Behaviour:
- vte 0.76: pressing backspace deletes the whole line (as configured 
with `bindkey`)
- vte 0.77: pressing backspace deletes only the last character (as if 
the configured `bindkey` wasn't seen)

## Example in nano

To reproduce:

- add `bind ^H replace main` to nanorc (e.g. ~/.config/nano/nanorc)
- open nano
- press a few characters to have something in the buffer to delete
- then…

Behaviour:
- vte 0.76: pressing ctrl-h pops the replace menu
- vte 0.77: pressing ctrl-h deletes the last character (as if `bind` 
wasn't seen)

## vte?

None of my terminals/zsh/nano/etc. configurations changed. I've tested 
several vte-based terminal, all expose the same bug. I've tested non-vte 
terminals, they work fine, unlike vte 0.77.91.