Remove deprecated `workspace_ids` argument from `r/tfe_variable_set`

[sebasslash]

Description

workspace_ids has been marked as a deprecated argument since v0.33.0. This PR omits the fix #628 in favor of fully removing the "apply to a workspace" logic from this resource. The reasoning for removing this attribute as an argument is two-fold:

• Using the workspace_ids argument would override any existing workspaces that used this variable set.
• The logic for creating a variable set was tightly coupled with applying it to a workspace(s) leading to some wonky behavior as noted in #628 . For ease of mind, these two operations should be separate to avoid any weird behavior. You can also read more in #537

workspace_ids will remain as a computed property in the resource. The recommended method to apply a variable set to a workspace remains r/tfe_workspace_variable_set.

[sebasslash]

I wouldn't mind holding off for now, but I'm curious as to why you'd want to maintain the deprecated status for another few months?

If we do hold off we'll need to merge #628 :+1:

[brandonc]

@sebasslash All deprecations need a healthy period of warning. Our official policy is no fewer than 6 months. I can provide links but not in GH comment.