remove API experiments from perlexperiment

As we discussed on p5p, these experiments are too many, too
undifferentiated, and already marked in the perlapi documentation.
perlexperiment: embedded code in regex not experimental

This was sorted out by 83f32abae and the thread found at
http://www.nntp.perl.org/group/perl.perl5.porters/2013/06/msg203129.html