vault: Remove legacy token based authentication workflow. (#25155)

The legacy workflow for Vault whereby servers were configured
using a token to provide authentication to the Vault API has now
been removed. This change also removes the workflow where servers
were responsible for deriving Vault tokens for Nomad clients.

The deprecated Vault config options used byi the Nomad agent have
all been removed except for "token" which is still in use by the
Vault Transit keyring implementation.

Job specification authors can no longer use the "vault.policies"
parameter and should instead use "vault.role" when not using the
default workload identity.

---------

Co-authored-by: Tim Gross <tgross@hashicorp.com>
Co-authored-by: Aimee Ukasick <aimee.ukasick@hashicorp.com>

testutil/vault.go

@@ -97,7 +97,6 @@ func NewTestVaultFromPath(t testing.T, binary string) *TestVault {
 		Config: &config.VaultConfig{
 			Name:    structs.VaultDefaultCluster,
 			Enabled: &enable,
-			Token:   token,
 			Addr:    http,
 		},
 	}
@@ -179,7 +178,6 @@ func NewTestVaultDelayedFromPath(t testing.T, binary string) *TestVault {
 		Client:    client,
 		Config: &config.VaultConfig{
 			Enabled: &enable,
-			Token:   token,
 			Addr:    http,
 		},
 	}