layers: fix calculation of intercepting functions.

Assign _gen_layer_get_global_extension_info to intercept.
Remove duplicate calculation of lookups.
diff --git a/vk-layer-generate.py b/vk-layer-generate.py
index cc30a22..ab11223 100755
--- a/vk-layer-generate.py
+++ b/vk-layer-generate.py
@@ -285,8 +285,7 @@
                     elif 'DbgUnregisterMsgCallback' == proto.name:
                         intercept = self._gen_layer_dbg_callback_unregister()
                     elif 'GetGlobalExtensionInfo' == proto.name:
-                        funcs.append(self._gen_layer_get_global_extension_info(self.layer_name))
-                        intercepted.append(proto)
+                        intercept = self._gen_layer_get_global_extension_info(self.layer_name)
                 if intercept is not None:
                     funcs.append(intercept)
                     intercepted.append(proto)
@@ -298,13 +297,6 @@
             lookups.append("    return (void*) %s%s;" %
                     (prefix, proto.name))
 
-        prefix="vk"
-        lookups = []
-        for proto in intercepted:
-            lookups.append("if (!strcmp(name, \"%s\"))" % proto.name)
-            lookups.append("    return (void*) %s%s;" %
-                    (prefix, proto.name))
-
         # add customized layer_intercept_proc
         body = []
         body.append("static inline void* layer_intercept_proc(const char *name)")