Remove support for extension loading in SQLite integrations

[aaronpowell]

Initially we prototyped the ability for the SQLite integration to load extensions either from local binaries or NuGet packages, in a case where you would specify that on the hosting integration using the WithNuGetExtension or WithLocalExtension methods.

This would then pass a bunch of metadata through the connection string that the client integrations would parse and load for you.

Unfortunately, this is clunky, as it results in an invalid connection string (see #690) and my original goal was to support the loading of https://www.nuget.org/packages/sqlite-vec/ - but this NuGet package now ships a source file that makes it easier to load the extension.

For the client integration, both the EF and Microsoft.Data.Sqlite, we need to remove the code that will try to read the Extensions part of the connection string, since that's being removed in the hosting integration, and then remove any associated code that will attempt to load the extensions.