Test: fix token bwc tests due to bad backport

This change fixes the token bwc tests that started failing after a bad
backport of #33106. During merge conflict resolution, an additional if
statement was added that used the incorrect passphrase in the keystore,
which caused token validation to fail. This if statement has been
removed in this commit.

Closes #33197

Author: jaymode

x-pack/qa/rolling-upgrade/build.gradle

@@ -215,9 +215,6 @@ subprojects {
           setting 'xpack.watcher.encrypt_sensitive_data', 'true'
           keystoreFile 'xpack.watcher.encryption_key', "${mainProject.projectDir}/src/test/resources/system_key"
         }
-        if (version.before('6.0.0')) {
-          keystoreSetting 'xpack.security.authc.token.passphrase', 'token passphrase'
-        }
       }
     }