Replace MethodDoc.[Ch] with generation at CMake time

[markcmiller86]

Is your feature request related to a problem?

MethodDoc.[Ch] are generated from .rst files. This allows us to have easily human readable and editable content documenting the CLI but still have that content appear in help(foo) from within the VisIt CLI python interpreter.

Having the generated files be part of our repo creates confusion especially for newbie or occasional developers. And, there is really no reason we need to keep the generated files in the repo.

Lets remove them from the repo and generate them at CMake time. This would eliminate any confusion over what to edit and eliminate the need for any CI (see proposed https://github.com/visit-dav/visit/pull/19879) too.