Drop explicit build and virtualenv installation from Pyodide build tools

[agriyakhetarpal]

See 0911b78 (#2775) and #2775 (comment): it is better that we remove build[virtualenv] from the top-level install command entirely. pyodide-build already declares build~=1.2.0 and virtualenv as direct dependencies, so they'll come in transitively at the right versions. cibuildwheel shouldn't be separately requesting build[virtualenv] for the Pyodide platform.

Perhaps, at some later point, we should vendor build into pyodide-build and drop the pins. I briefly recall some conversations about this with @ryanking13 (not sure where that was?).

[ryanking13]

Perhaps, at some later point, we should vendor build into pyodide-build and drop the pins. I briefly recall some conversations about this with @ryanking13 (not sure where that was?).

Not sure if we want to vendor the whole build package to pyodide-build, but I think we can relax the pin to make it more flexible. We've removed all usage of the private methods, so I think it is quite stabler than before when we first started using it.

[agriyakhetarpal]

I think we can relax the pin to make it more flexible. We've removed all usage of the private methods, so I think it is quite stabler than before when we first started using it.

This is indeed what I was working on in the past hour; sounds good to me!