Remove outdated QSS implementation

Author: lochel

openmodelica/bootstrapping/LoadCompilerSources.mos

@@ -122,7 +122,6 @@ if true then /* Suppress output */
     prefixPath + "BackEnd/BackendDAEUtil.mo",
     prefixPath + "BackEnd/BackendDump.mo",
     prefixPath + "BackEnd/BackendEquation.mo",
-    prefixPath + "BackEnd/BackendQSS.mo",
     prefixPath + "BackEnd/BackendVariable.mo",
     prefixPath + "BackEnd/BackendVarTransform.mo",
     prefixPath + "BackEnd/BinaryTree.mo",
@@ -193,7 +192,6 @@ if true then /* Suppress output */
     prefixPath + "Template/CodegenJava.mo",
     prefixPath + "Template/CodegenJS.mo",
     prefixPath + "Template/CodegenModelica.mo",
-    prefixPath + "Template/CodegenQSS.mo",
     prefixPath + "Template/CodegenUtil.mo",
     prefixPath + "Template/CodegenXML.mo",
     prefixPath + "Template/DAEDumpTpl.mo",