Deprecate "primaryKey".

PiperOrigin-RevId: 547121954
Change-Id: I35a3ac63dcd2492bc241996e1632257d38433195

Author: tholenst

src/main/java/com/google/crypto/tink/KeysetHandle.java

@@ -1164,7 +1164,10 @@ public <P> P getPrimitive(Class<P> targetClassObject) throws GeneralSecurityExce
    * wrapped in a {@code KeyHandle}.
    *
    * <p>Please do not use this function in new code. Instead, use {@link #getPrimary}.
+   *
+   * @deprecated Use {@link #getPrimary} instead.
    */
+  @Deprecated
   public KeyHandle primaryKey() throws GeneralSecurityException {
     int primaryKeyId = keyset.getPrimaryKeyId();
     for (Keyset.Key key : keyset.getKeyList()) {