Remove SQL Server upgrade scripts and code

[labkey-jeckels]

Rationale

We no longer support SQLServer as a primary DB

Changes

• Remove schema upgrade scripts
• Remove SQLServer conditional code
• Remove SupportedDatabases in module.properties
• Remove uses of PostgresOnlyTest
• Create Postgres version of covidseq schema

[labkey-jeckels]

@bbimber the interesting thing for this repo is the covidseq module. It had no Postgres upgrade scripts. I did a trivial port (to be verified by TeamCity) to prevent schema validation failures. If this is a module worth migrating, you'll want to backport these changes to 26.3 or 26.7 so there's something to migrate into.