ref-manual: Edits to cmake class.

(From yocto-docs rev: aa397e791e02f3a5e3d9d2df40f298cbf4f26fe2)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -379,7 +379,7 @@
     <title><filename>cmake.bbclass</filename></title>
 
     <para>
-        The CMake build system (<filename>cmake</filename>) class allows for
+        The <filename>cmake</filename> class allows for
         recipes that need to build software using the CMake build system.
         You can use the
         <link linkend='var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></link>