Use SQLDelight for inserts instead of KeychainProvider

OpenKeychain/src/main/sqldelight/org/sufficientlysecure/keychain/KeySignatures.sq

@@ -5,6 +5,9 @@ CREATE TABLE IF NOT EXISTS key_signatures (
     FOREIGN KEY(master_key_id) REFERENCES keyrings_public(master_key_id) ON DELETE CASCADE
 );
 
+insertKeySignature:
+INSERT INTO key_signatures VALUES (?, ?);
+
 selectMasterKeyIdsBySigner:
 SELECT master_key_id
    FROM key_signatures WHERE signer_key_id IN ?;