Remove deprecated APIs

[morozov]

Q	A
BC Break	yes

1. A coding standard violation is fixed (looks introduced by Manually merge 2.11.x into 3.0.x #4275).
2. DBALException was deprecated in Deprecate DBAL\DBALException in favor of DBAL\Exception #4253.
3. AbstractPlatform::supportsForeignKeyOnUpdate() is removed. Originally it was removed in Remove deprecated APIs #4234 but then mistakenly reintroduced in Manually merge 2.11.x into 3.0.x #4275.
4. Back-ported Remove Doctrine\DBAL\Types\Type::getDefaultLength() #3255 from master.

[greg0ire]

I think I read somewhere that the CodeCov message only appears on lines with exceptions (technically, you exit the method kinda before reaching its end).

[morozov]

I believe it's just that code is not covered. And in fact dead code as of f580f0a (should be deprecated and removed if not already done in master).