don't print so many errors for same decision

As a result, alternative(s) 2 were disabled for that input
java.g:76:16: Decision can match input such as "RCURLY" using multiple
alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input
java.g:76:16: Decision can match input such as "SEMICOLON" using
multiple alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input
java.g:76:16: Decision can match input such as "WHILE" using multiple
alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input
java.g:76:16: Decision can match input such as "PRIVATE" using
multiple alternatives: 1, 2

they are all the same error, just different input sequence.