Called when ELIMINATE command needs to be parsed from within the CHARACTERS block.
Deals with everything after the token ELIMINATE up to and including the semicolon that terminates the ELIMINATE command. Any character numbers or ranges of character numbers specified are stored in the NxsUnsignedSet `eliminated', which remains empty until an ELIMINATE command is processed. Note that like all sets the character ranges are adjusted so that their offset is 0. For example, given "eliminate 4-7;" in the data file, the eliminate array would contain the values 3, 4, 5 and 6 (not 4, 5, 6 and 7). It is assumed that the ELIMINATE command comes before character labels and/or character state labels have been specified; an error message is generated if the user attempts to use ELIMINATE after a CHARLABELS, CHARSTATELABELS, or STATELABELS command.