stop supporting to VS 2019

[mszhanyi]

Description

Remove VS 2019 code.

Motivation and Context

[AndreyOrb]

Well, this commit together with some other issue (that no one could predict) turned out to be a problem.

Here's the problem:
There's still a general support for CUDA 11.8 in ORT, but because of this limitation, only Visual Studio 2019 or Visual Studio 2022 v17.9.2 (or less) can still compile the CUDA 11.8

In my case, I must be able to build ORT with both CUDA 11.8 and CUDA 12.x (as separate ORT builds, of course).

From different resources (microsoft, microsoft) I learned that several VS versions with the same major version can be installed.
Then, I will probably have to run build.bat from the correct VS CMD (unverified).

For now, the easiest way for me to solve the problem was to add back "Visual Studio 16 2019" in build.py.
This way, I can build ORT with CUDA 11.8 using --cmake_generator "Visual Studio 16 2019" --compile_no_warning_as_error

Just wanted to leave this info somewhere for the future generations ;)

[snnn]

After we removed this flag, we still built CUDDA 11.8 with VS 2022 and it did work well. Therefore I think we do not have to keep the VS 2019 there.