Rename helm-projectile-switch-to-eshell -> helm-projectile-switch-to-shell

[leungbk]

helm-ff-switch-to-eshell is not defined, but helm-ff-switch-to-shell is. By default, it uses Eshell.

An alternative is to keep helm-projectile-switch-to-eshell's name unchanged and simply change the two lines where helm-ff-switch-to-eshell (which doesn't exist) is invoked.

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Thanks!

[bbatsov]

Thanks!