bpo-30726: PCbuild _elementtree: remove duplicate defines (#2348)

bpo-30726, bpo-29591: libexpat 2.2.1 of Modules/expat/ now uses
a winconfig.h configuration file which already defines:

* XML_NS
* XML_DTD
* BYTEORDER=1234
* XML_CONTEXT_BYTES=1024
* HAVE_MEMMOVE

Remove these defines from PCbuild/_elementtree.vcxproj to prevent
compiler warnings.

Co-Authored-By: Jeremy Kloth <jeremy.kloth@gmail.com>

PCbuild/_elementtree.vcxproj

@@ -62,7 +62,7 @@
   <ItemDefinitionGroup>
     <ClCompile>
       <AdditionalIncludeDirectories>..\Modules\expat;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-      <PreprocessorDefinitions>XML_NS;XML_DTD;BYTEORDER=1234;XML_CONTEXT_BYTES=1024;USE_PYEXPAT_CAPI;XML_STATIC;HAVE_MEMMOVE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>USE_PYEXPAT_CAPI;XML_STATIC;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>
     <Link>
       <BaseAddress>0x1D100000</BaseAddress>
@@ -103,4 +103,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>