py, extmod: Remove include of unnecessary system headers.
diff --git a/py/objfloat.c b/py/objfloat.c
index 2e8b7f7..b94caf3 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -28,7 +28,6 @@
 #include <stdio.h>
 #include <string.h>
 #include <assert.h>
-#include <math.h>
 
 #include "py/nlr.h"
 #include "py/parsenum.h"
@@ -37,6 +36,8 @@
 
 #if MICROPY_PY_BUILTINS_FLOAT
 
+#include <math.h>
+
 #if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
 #include "py/formatfloat.h"
 #endif