Remove unused mysqlnd options

[kamil-tekiela]

MYSQL_OPT_WRITE_TIMEOUT was a noop as this was never implemented.
The protocol options were introduced in ebaee8a and it's unclear if they ever were used or what they were meant for.

[bukka]

I don't think we should be dropping those even though they are not used right now.

[kamil-tekiela]

I don't think we should be dropping those even though they are not used right now.

Ok, but is there a good reason to keep them? We cannot document them in the PHP manual because they don't do anything and it's unlikely that they will ever be reused in the future.

[Girgias]

I don't think we should be dropping those even though they are not used right now.

Why? Having a non-existing implementation is completely useless, and on top of that if someone wants to add missing protocol functionality they are going to assume that all the existing options are actually implemented.

Moreover, this has no impact on PHP userland as you cannot "directly" access MySQLnd drivers data AFAIK.

[bukka]

I understand what it is. I just don't think we need to remove bits that can be potentially useful. They are just definitions for potential later use. So I just don't see reason to remove it. But I don't really feel strongly about this so don't take it as a blocker for merging.