Remove redundant assertions

Author: jordan-powers

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/extras/MatchOnlyTextFieldMapper.java

@@ -389,7 +389,6 @@ protected BytesRef storedToBytesRef(Object stored) {
                         if (stored instanceof BytesRef) {
                             return (BytesRef) stored;
                         } else {
-                            assert stored instanceof String;
                             return new BytesRef((String) stored);
                         }
                     }
@@ -485,7 +484,6 @@ protected void write(XContentBuilder b, Object value) throws IOException {
                     if (value instanceof BytesRef) {
                         b.value(((BytesRef) value).utf8ToString());
                     } else {
-                        assert value instanceof String;
                         b.value((String) value);
                     }
                 }

server/src/main/java/org/elasticsearch/index/mapper/BlockStoredFieldsReader.java

@@ -83,7 +83,6 @@ protected BytesRef toBytesRef(Object v) {
                     if (v instanceof BytesRef) {
                         return (BytesRef) v;
                     } else {
-                        assert v instanceof String;
                         return BlockSourceReader.toBytesRef(scratch, (String) v);
                     }
                 }