Chain length adjustment
You are reducing the minimum length of chain required by 1 link. (i.e. 22 teeth vs 21 teeth on the front chainring.) 

Unless the initial chain sizing was overly generous, you should not notice any significant difference in that small a chainring size change. Since you can only remove 2 links, not just the one link you are changing, you are likely already in 
the appropriate zone for chain length.