Disable buttons interaction (backspace) in Filter Editor

[Chinaski1]

Steps to reproduce

1. Open AdGuard settings -> AdBlocker section -> Filter editor
2. Choose Base (or any other filter) -> Choose one of the filtering rules
3. Press Backspace
4. Click on any other rule
5. The rule should not disappear when you press Backspace

Screenshot:

• AdGuard version: 7.6 nightly 11 (build 3447, CL 1.7.153)