xgl.py: remove icd_dispatch_table

Its role was replaced by XGL_LAYER_DISPATCH_TABLE defined in xglLayer.h but it
was still used as "a list of all protoype names".  Add proto_names for that
purpose.
diff --git a/xgl-layer-generate.py b/xgl-layer-generate.py
index b8c7cf2..5999aeb 100755
--- a/xgl-layer-generate.py
+++ b/xgl-layer-generate.py
@@ -551,7 +551,7 @@
             for ext_name in extensions:
                 func_body.append('    else if (!strncmp("%s", funcName, sizeof("%s")))\n'
                                  '        return %s;' % (ext_name, ext_name, ext_name))
-        for name in xgl.icd_dispatch_table:
+        for name in xgl.proto_names:
             if name == "GetProcAddr":
                 continue
             if name == "InitAndEnumerateGpus":
@@ -578,7 +578,7 @@
                          '    fpNextGPA = pCurObj->pGPA;\n'
                          '    assert(fpNextGPA);\n');
 
-        for name in xgl.icd_dispatch_table:
+        for name in xgl.proto_names:
             func_body.append('    %sType fp%s = fpNextGPA((XGL_PHYSICAL_GPU) pCurObj->nextObject, (XGL_CHAR *) "%s%s");\n'
                              '    nextTable.%s = fp%s;' % (name, name, prefix, name, name, name))