Mysql: Remove symbolic-links=0 in the MySQL 8.0 image configuration to avoid warning

[vmassol]

See https://github.com/docker-library/mysql/blob/bc6e37a2bed792b1c4fc6ab1ec3ce316e6a5f061/8.0/config/my.cnf#L28

This leads to the following when running the image:

2020-05-28T23:49:45.213689Z 0 [Warning] [MY-011070] [Server] 'Disabling symbolic links using --skip-symbolic-links (or equivalent) is the default. Consider not using this option as it' is deprecated and will be removed in a future release.

Would be great to remove it to avoid the warning.

Thanks!

[tianon]

Yep, see #677 :+1:

[vmassol]

hey hi @tianon :) Cool, and sorry for the dup!