Remove BUILDING_NOTE_EXTENSION from docs

Author: nightlark

Doc/Manual/Preprocessor.html

@@ -121,7 +121,6 @@ <H2><a name="Preprocessor_condition_compilation">10.3 Conditional Compilation</a
 SWIGJAVASCRIPT                  Defined when using Javascript
 SWIG_JAVASCRIPT_JSC             Defined when using Javascript for JavascriptCore
 SWIG_JAVASCRIPT_V8              Defined when using Javascript for v8 or node.js
-BUILDING_NODE_EXTENSION         Defined when using Javascript for node.js
 SWIGLUA                         Defined when using Lua
 SWIGMZSCHEME                    Defined when using Mzscheme
 SWIGOCAML                       Defined when using OCaml