In regparse.c, in function node_extended_grapheme_cluster,
we used a raw if() with exit(1) as a cross-check for our
length calculations for the common node array. Convert this
to an assertion and comment it out because it is not needed
for active code.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66269 b2dd03c8-39d4-4d8f-98ff-823fe69b080e