drop hardcoded -O3

Index: methods.py
--- methods.py.orig
+++ methods.py
@@ -126,8 +126,6 @@ def force_optimization_on_debug(self):
         return
     elif self.msvc:
         self["OPTIMIZELEVEL"] = "/O2"
-    else:
-        self["OPTIMIZELEVEL"] = "-O3"
 
 
 def add_module_version_string(self, s):
