Remove InnoDB 5.7 version number from MariaDB 10.3 onwards

Because the InnoDB implementation in MariaDB has diverged from MySQL, it is not meaningful to report a MySQL version number for InnoDB any more. Some examples:

• MariaDB 10.1 (which is based on MySQL 5.6) included encryption and variable-size page compression before MySQL 5.7 introduced them
• MariaDB 10.2 (based on MySQL 5.7) introduced persistent AUTO_INCREMENT (MDEV-6076) in a GA release before MySQL 8.0
• MariaDB 10.3 (based on MySQL 5.7) introduced instant ADD COLUMN (MDEV-11369) before MySQL

All of these features use a different implementation and file format. Also, some features were never merged from MySQL 5.7, and thus MariaDB is not affected by related bugs. Examples include CREATE TABLESPACE and the reimplementation of the partitioning engine.