Remove duplicated C compiler option from tests that is already set by the test...

Remove duplicated C compiler option from tests that is already set by the test runner via the cpp11 tag.

tests/run/cpp_classes_def.pyx

 # mode: run
-# tag: cpp, werror
+# tag: cpp, werror, cpp11
 # cython: experimental_cpp_class_def=True
-# distutils: extra_compile_args=-std=c++0x
 
 cdef double pi
 from math import pi

tests/run/cpp_smart_ptr.pyx

 # mode: run
 # tag: cpp, werror, cpp11
-# distutils: extra_compile_args=-std=c++0x
 
 from libcpp.memory cimport unique_ptr, shared_ptr, default_delete, dynamic_pointer_cast
 from libcpp cimport nullptr

tests/run/cpp_stl_conversion.pyx

 # mode: run
-# tag: cpp, werror
-# distutils: extra_compile_args=-std=c++0x
+# tag: cpp, werror, cpp11
 
 import sys
 from libcpp.map cimport map

tests/run/cpp_stl_cpp11.pyx

 # mode: run
 # tag: cpp, werror, cpp11
-# distutils: extra_compile_args=-std=c++0x
 
 import sys
 from libcpp.unordered_map cimport unordered_map

tests/run/cpp_stl_function.pyx

-# distutils: extra_compile_args=-std=c++0x
 # mode: run
-# tag: cpp
+# tag: cpp, cpp11
 
 from libcpp.functional cimport function
 cimport cpp_function_lib

tests/run/cpp_stl_string_cpp11.pyx

 # mode: run
 # tag: cpp, werror, cpp11
-# distutils: extra_compile_args=-std=c++11
 
 from libcpp.string cimport string