The function get_wkb_of_default_point() should never have been
added, and the cleanup in commit 56ff6f1b
should have removed it.

The unnecessary code was added in
mysql/mysql-server@0a27b72171c4449f506ad4e93df8c29fead1ed72
and mostly disabled in
mysql/mysql-server@8f11af7734509821b654f2c330dff5374c89073c.

In MariaDB, the types DATA_POINT and DATA_VAR_POINT are never used.
Instead, DATA_GEOMETRY continues to be used since 10.2.2, introduced by
mysql/mysql-server@673bad7c7e17701b69e29d0fbc4e2d68c1a7b613
in MySQL 5.7.1.