[maven-release-plugin] prepare release thymeleaf-spring4-2.0.21
Revert "[maven-release-plugin] prepare release thymeleaf-spring4-2.0.21"

This reverts commit 065ac74173653cf45eabd8af042866d06d7a9e36.
Revert "[maven-release-plugin] prepare for next development iteration"

This reverts commit 380af4d72dc4bf2e50c4c69d31bb18dec8156ebc.