Rule and Raven says "Prior to 1983, a priest could absolve the sin and remove the excommunication."

1917 CIC 2350 reserved lifting of the sanction (excommunication) to the ordinary.  
1917 CIC 2350: http://www.intratext.com/IXT/LAT0813/_P8J.HTM

1983 CIC 1398 does not include that limitation. 
1983 CIC 1398: http://www.vatican.va/archive/ENG1104/__P57.HTM