Re-add warning suppression
The IDE doesn't think this suppression is needed, but javac has a
warning and we have -Werror enabled.
HitHashMapOfCollection.java:30: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
protected Statistics<K> statistics;
^
Change-Id: I2d1c4d6ef8ff58b0ef6e3f2a9cb80003e4e7d3b8