Revert github_branch_protection GraphQL Implementation

[jcudit]

This reverts the github_branch_protection resource back to the v3.0.0 implementation, reverting the GraphQL implementation merged in https://github.com/terraform-providers/terraform-provider-github/pull/337.

Migration from v3.0.0 to this version has been tested and requires no configuration changes.

$ TF_LOG=TRACE terraform plan
...
2020/11/01 15:02:52 [TRACE] UpgradeResourceState: upgrading state for github_branch_protection.test from version 0 to 2 using provider "registry.terraform.io/-/github"
...
No changes. Infrastructure is up-to-date.

Migration from v3.1.0 to the next release has been tested and requires the following example configuration changes:

# v3.1.0

resource "github_branch_protection" "test" {

  repository_id = github_repository.test.node_id
  pattern       = "main"

  push_restrictions = [
    github_team.first.node_id, github_team.second.node_id,
  ]

}

# next release

resource "github_branch_protection" "test" {

  repository = github_repository.test.name
  branch     = "main"

  restrictions {
    users = []
    teams = [github_team.first.slug, github_team.second.slug]
    apps  = []
  }

}

$ TF_LOG=TRACE terraform plan
...
2020/11/01 15:09:58 [TRACE] UpgradeResourceState: upgrading state for github_branch_protection.test from version 1 to 2 using provider "registry.terraform.io/-/github"
...
Apply complete! Resources: 0 added, 1 changed, 0 destroyed.

/cc https://github.com/terraform-providers/terraform-provider-github/issues/566

[jcudit]

Closing this as we've discussed rolling forward with v4.0.0 instead.