Replace gradle-witness with checksum-dependency plugin

bramble-android/build.gradle

bramble-api/build.gradle

bramble-api/witness.gradle

bramble-core/build.gradle

bramble-core/witness.gradle

bramble-java/build.gradle

bramble-java/witness.gradle

briar-android/build.gradle

briar-android/witness.gradle

briar-api/build.gradle

briar-api/witness.gradle

briar-core/build.gradle

briar-core/witness.gradle

briar-headless/build.gradle

briar-headless/witness.gradle

build.gradle

checksum.xml

gradle.properties

libs/gradle-witness.jar

settings.gradle