Remove more Oracle and Mssql leftovers

Remove more Oracle and Mssql leftovers

Follows-up 4d10bb14e81 and 807d793ab9079.

According to codesearch [0], these were the last usages. Note that this
patch leaves two constants in places, IDatabase::DBO_SYSDBA and
DBO_DDLMODE. These are public constants used "mostly for oracle" according
to the docs, but maybe we could find other use cases in the future (?).

[0] - https://codesearch.wmflabs.org/core/?q=oracle%7Cmssql&i=fosho&files=%5C.%5B%5Ej%5Cd%5D%7Cen%5C.json&repos=

Bug: T230418
Change-Id: Ibfb748b4b23b885a77f4de161af4bf2ab9649a89