Remove Drake exception allowing for -inl.h files

We typically no longer allow these files.

Author: jwnimmer-tri

cppguide.html

@@ -213,10 +213,6 @@ <h3 id="Self_contained_Headers">Self-contained Headers</h3>
 <p>Header files should be self-contained (compile on their own) and
 end in <code>.h</code>.  Non-header files that are meant for inclusion
 should end in <code>.inc</code> and be used sparingly.</p>
-<p class="exception drake">
-  The Self-contained headers rule may be disobeyed when implementing
-  the <a href="http://drake.mit.edu/cxx_inl.html#cxx-inl-files">C++ *-inl.h
-  files pattern</a> in its exact form.</p>
 </div> 
 
 <div class="stylebody">