drop hardcoded -O3

Index: methods.py
--- methods.py.orig
+++ methods.py
@@ -105,8 +105,6 @@ def force_optimization_on_debug(self):
         self["CFLAGS"] = [x for x in self["CFLAGS"] if not x.startswith("/O")]
         self["CXXFLAGS"] = [x for x in self["CXXFLAGS"] if not x.startswith("/O")]
         self.AppendUnique(CCFLAGS=["/O2"])
-    else:
-        self.AppendUnique(CCFLAGS=["-O3"])
 
 
 def add_module_version_string(self, s):
