Remove an unintentional change committed in r1443783.

* subversion/bindings/swig/perl/libsvn_swig_perl/swigutil_pl.h
  (#undef _): Remove.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1445277 13f79535-47bb-0310-9956-ffa450edef68