Update references to WildFlyElytronProvider in the Elytron documentation

When Elytron was converted to a multi-module project, WildFlyElytronProvider was deprecated and provider implementations were added for the individual modules (e.g., WildFlyElytronPasswordProvider, WildFlyElytronCredentialStoreProvider, etc.). However, the Elytron security guide still references the deprecated WildFlyElytronProvider class instead of referencing the new provider implementations. This should be updated.