refactor: remove unused text resources

[NathanBaulch]

Stumbled on an unused text resource, so I wrote the following bash+ripgrep command to find all 12.

rg 'Key="Text\.([^"]+)"' -Nor '$1' ./src/Resources/Locales/en_US.axaml \
    | xargs -I {} bash -c 'if ! rg -qFw --glob "!src/Resources/Locales/**" "{}"; then echo "{}"; fi'