UnTrain - decrementaal learning (untraining) of classifier
CC = untrain_sc(CC,classlabel,x)
CC is a statistical classifier, it contains basically the mean
and the covariance of the data of each class. This information
is incoded in the so-called "extended covariance matrices".
CC can be used for various statistical classifiers included
LDA, MDA, QDA, GRB, etc.
see also: TEST_SC, COVM, LDBC2, LDBC3, LDBC4, MDBC, GDBC