chore: Remove unused code

Author: lqiu96

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/JsonToProtoMessage.java

@@ -709,7 +709,7 @@ private void fillField(
               protoMsg.setField(fieldDescriptor, value);
             }
           } else if (val instanceof Short || val instanceof Integer || val instanceof Long) {
-            protoMsg.setField(fieldDescriptor, ((Long) val).toString());
+            protoMsg.setField(fieldDescriptor, String.valueOf(val));
           } else if (val instanceof Timestamp) {
             Timestamp timestamp = (Timestamp) val;
             protoMsg.setField(
@@ -1001,7 +1001,7 @@ private void fillRepeatedField(
                 protoMsg.addRepeatedField(fieldDescriptor, value);
               }
             } else if (val instanceof Short || val instanceof Integer || val instanceof Long) {
-              protoMsg.setField(fieldDescriptor, ((Long) val).toString());
+              protoMsg.setField(fieldDescriptor, String.valueOf(val));
             } else if (val instanceof Timestamp) {
               Timestamp timestamp = (Timestamp) val;
               protoMsg.addRepeatedField(
@@ -1101,17 +1101,4 @@ static boolean isValidTimestamp(String timestamp) {
     }
     return true;
   }
-
-  /**
-   * Converts microseconds from epoch to a Java Instant.
-   *
-   * @param microsFromEpoc the number of microseconds from 1970-01-01T00:00:00Z
-   * @return the Instant corresponding to the microseconds
-   */
-  private static Instant fromEpochMicros(long microsFromEpoc) {
-    long seconds = Math.floorDiv(microsFromEpoc, MICROS_PER_SECOND);
-    int nanos = (int) Math.floorMod(microsFromEpoc, MICROS_PER_SECOND) * NANOS_PER_MICRO;
-
-    return Instant.ofEpochSecond(seconds, nanos);
-  }
 }