Remove support for CAIN

[smcintyre-r7]

Per this conversation:

(CAIN) is a thing from the past, I don't think it should still be supported in metasploit.

It makes sense to drop support for it and remove all references from modules and documentation.

[github-actions]

Hi!

This issue has been left open with no activity for a while now.

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[SaiSakthidar]

I would like to work on this issue

[smcintyre-r7]

It should be as simple as iteratively removing all references to cain starting with the datastore option CAINPWFILE then making sure the tests still pass.

[SaiSakthidar]

@smcintyre-r7
Done , ive linked the PR