ci,CMake: Drop Conan support for vcpkg

Between packages breaking, Conan always being a moving target for
minimum required CMake support, and now their moves to Conan 2.0 causing
existing packages to break, I suppose this was a long time coming. vcpkg
isn't without its drawbacks, but at the moment it seems easier on the
project to use for external packages.

Mostly removes the logic for Conan from the root CMakeLists file,
leaving basic find_package()'s in its place. Sets only the
find_package()'s that require CONFIG mode as necessary. clang and linux
CI now use the vcpkg toolchain file configured in the Docker container
when possible.

mingw CI turns off YUZU_TESTS because there's no way on the container to
run Windows executables on a Linux host anyway, and it's not easy to get
Catch2 there.