Remove unused resources.

briar-android/src/main/res/drawable/ic_emoji_activity.xml

...android/src/main/res/drawable/ic_emoji_animals_nature.xml

briar-android/src/main/res/drawable/ic_emoji_emoticons.xml

briar-android/src/main/res/drawable/ic_emoji_flags.xml

briar-android/src/main/res/drawable/ic_emoji_food_drink.xml

briar-android/src/main/res/drawable/ic_emoji_objects.xml

briar-android/src/main/res/drawable/ic_emoji_recent.xml

...-android/src/main/res/drawable/ic_emoji_smiley_people.xml

briar-android/src/main/res/drawable/ic_emoji_symbols.xml

...-android/src/main/res/drawable/ic_emoji_travel_places.xml

briar-android/src/main/res/values/emoji.xml