Eliminate need to insert into SchemaVersion table at start of "full" migration script

[johnstairs]

We should be able to eliminate this from the start of every 6.sql, 7.sql, etc file:

/*************************************************************
    Schema Version
**************************************************************/

INSERT INTO dbo.SchemaVersion
VALUES
    (6, 'started')

GO

Instead, we could insert the row before calling the script, like we do for .diff.sql scripts.

[rbans96]

Created #AB76682.