bases/py-MySQLdb: Fix build with MariaDB 10.2.7

With MariaDB 10.2.6 the Connect/C is updated to ~3.0. This means the C interface changed slightly and some functions are changed.

• Replace direct struct access with accessor in _mysql.c
• Add LICENSE/LICENSE_FILE
• Strip Binaries
• Remove conflict with itself

PR: 219797
Reviewed_by: sunpoet, koobs, brnrd
Submitted by: sirl33tname@gmail.com
Approved by: koobs (python)
Differential Revision: https://reviews.freebsd.org/D11054