remove xml-apis.jar from product distributions

Classes from this JAR are included into rt.jar from JRE 1.8, and when there are two versions of them in the classpath it may lead to problems with classloading (e.g. IDEA-176725). Now IDEs and external build process are started under Java 8 so we don't need this JAR anymore.

.idea/libraries/Xerces.xml

@@ -2,7 +2,6 @@
   <library name="Xerces">
     <CLASSES>
       <root url="jar://$PROJECT_DIR$/lib/xercesImpl.jar!/" />
-      <root url="jar://$PROJECT_DIR$/lib/xml-apis.jar!/" />
     </CLASSES>
     <JAVADOC />
     <SOURCES>

build/gant.xml

@@ -37,7 +37,6 @@
        <include name="snappy-in-java-*.jar"/>
        <include name="cli-parser-*.jar"/>
        <include name="nanoxml-*.jar"/>
-       <include name="xml-apis.jar"/>
        <include name="aether-*-all.jar"/>
        <include name="maven-aether-provider-*-all.jar"/>
        <include name="httpclient-*.jar"/>