Removed deprecated options for symbolic links.

[lrf141]

Overview

https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-2.html
symbolic-links=0 is deprecated in 8.0.2 and later versions.
This option will be removed in the future.

https://dev.mysql.com/doc/refman/8.0/en/symbolic-links-to-tables.html
We don't need to specify this option, as it is also disabled by default.
As long as this setting is specified, unnecessary warnings occur when the container is launched, so I removed it.

Expected Logs

↓Exist symbolic-links=0

2020-05-26 00:45:26+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.20-1debian10 started.
2020-05-26 00:45:26+00:00 [Note] [Entrypoint]: Switching to dedicated user 'mysql'
2020-05-26 00:45:26+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.20-1debian10 started.
2020-05-26 00:45:26+00:00 [Note] [Entrypoint]: Initializing database files
2020-05-26T00:45:26.849271Z 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.
2020-05-26T00:45:26.849849Z 0 [System] [MY-013169] [Server] /usr/sbin/mysqld (mysqld 8.0.20) initializing of server in progress as process 45

↓ Remove symbolic-links=0

2020-05-26 00:38:38+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.20-1debian10 started.
2020-05-26 00:38:38+00:00 [Note] [Entrypoint]: Switching to dedicated user 'mysql'
2020-05-26 00:38:38+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.20-1debian10 started.
2020-05-26 00:38:38+00:00 [Note] [Entrypoint]: Initializing database files
2020-05-26T00:38:38.794793Z 0 [System] [MY-013169] [Server] /usr/sbin/mysqld (mysqld 8.0.20) initializing of server in progress as process 44

It is expected that the warning on line 5 will not be output.

[tianon]

LGTM

cc @ltangvald

[ltangvald]

LGTM!