pdo_firebird: Cleanup code.

[sim1984]

Since Firebird PDO now requires fbclient 3.0+ to compile, some conditional compilation directives are no longer needed in the code.

[mlocati]

About eed7d2d: what about restoring a dump? In this case, we may have rather big queries, right?

[sim1984]

No. There is no support INSERT...VALUES with multiple entries. And it is not customary to do dumps there through a script like MySQL. But there may be a large EXECUTE BLOCK or DDL to create a PSQL PACKAGE BODY.
In any case, the error will be reported by fbclient or firebird server itself. There will be no buffer overflow.

[cmb69]

While I don't understand the SQL_TEXT to SQL_VARYING conversion that already happens, I trust you on this. Generally, this PR looks good to me.

Note that the Windows CI failure is unrelated (see PR#15518).

[sim1984]

While I don't understand the SQL_TEXT to SQL_VARYING conversion that already happens, I trust you on this.

This is done for the purpose of unification. For other data types, we also convert them to SQL_TEXT if a string is supplied as a parameter. This code is shorter, and at the same time allows empty strings to be treated as NULL for enumerated data types.

[cmb69]

@SakiTakamachi, if you have no objections, I'll merge this tomorrow.

[SakiTakamachi]

I had been in poor health for a long time.

This makes sense to me.

[cmb69]

Get well soon @SakiTakamachi! :)