Removed FindXercesC now that new versions of Xerces are integrated with cmake

This merge request is needed on the LHCb side when we use the DD4hep geometry framework and does not harm otherwise in the head of master.

The key questions are :

• does it break some backward compatibility ?
• do other (Atlas ?) have trouble with this change ?

GaudiUtils/CMakeLists.txt

@@ -57,7 +57,7 @@ endif()
 # Hide some Boost/ROOT/XercesC compile time warnings
 include_directories( SYSTEM ${Boost_INCLUDE_DIRS} ${ROOT_INCLUDE_DIRS} )
 if( XERCESC_FOUND )
-   include_directories( SYSTEM ${XERCESC_INCLUDE_DIRS} )
+   include_directories( SYSTEM ${XercesC_INCLUDE_DIRS} )
 endif()
 
 #---Libraries---------------------------------------------------------------