Remove ASP.NET Core 2 docs

[jamescrosswell]

Description

https://docs.sentry.io/platforms/dotnet/guides/aspnetcore/configuration/options/#MaxRequestBodySize
.NET Core 2.0 is very, very outdated.. just adding noise at this point.

[linear]

NET-580

[Flash0ver]

Shall we be more specific about the support policy for ASP.NET Core 2.3 on .NET Framework?
And instead remove ASP.NET Core 3.0?