_mongoc_write_command_init_insert and _mongoc_write_command_insert_append differ unnecessarily from the equivalent helper functions for update and remove: the insert functions take an array of documents instead of a single document.

(The inconsistency dates from the implementation of mongoc_collection_insert_bulk, now deprecated. In any case, mongoc_collection_insert_bulk can be responsible for handling an array of documents instead of pushing that chore down the call stack.)