Remove previously deprecated methods and options.

Deprecated configuration options removed as part of this ticket

• network_timeout (both as a client option and query option)
• safe (both as a client option and an option for insert, save, update, and remove)
• slaveOk/slave_okay (both as a client option and a query option)
• compile_re support is removed from all methods that supported it in the bson, gridfs, and pymongo modules. BSON regular expressions will always decode to bson.regex.Regex.
• secondaryAcceptableLatencyMS renamed localThresholdMS and changed to a global immutable option.

Deprecated methods removed as part of this ticket

• set_lasterror_options (on MongoClient, Database, and Collection)
• get_lasterror_options (on MongoClient, Database, and Collection)
• unset_lasterror_options (on MongoClient, Database, and Collection)

See the PyMongo 3.0 changelog for a comprehensive list of all other API changes.