Replace Throwables.propagate with equivalent "throw e" or "throw new RuntimeException(e)."

We are removing all calls in preparation for deleting the method.

More information: []

Tested:
    TAP --sample for global presubmit queue
    []
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117628955

java/com/google/domain/registry/model/registrar/Registrar.java

@@ -37,7 +37,6 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 import com.google.common.base.Predicate;
 import com.google.common.base.Predicates;
 import com.google.common.base.Supplier;
-import com.google.common.base.Throwables;
 import com.google.common.collect.FluentIterable;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -554,7 +553,7 @@ public class Registrar extends ImmutableObject implements Buildable, Jsonifiable
               (password + salt).getBytes(UTF_8)));
     } catch (NoSuchAlgorithmException e) {
       // All implementations of MessageDigest are required to support SHA-256.
-      throw Throwables.propagate(e);
+      throw new RuntimeException(e);
     }
   }