Remove the following BSON functions:

• MongoDB\BSON\fromJSON
• MongoDB\BSON\fromPHP
• MongoDB\BSON\toCanonicalExtendedJSON
• MongoDB\BSON\toJSON
• MongoDB\BSON\toPHP
• MongoDB\BSON\toRelaxedExtendedJSON

MongoDB\BSON\toJSON() is the only function without a direct equivalent on the Document class, but the legacy extended JSON format is already deprecated so there's no need to preserve that functionality.