remove superfluous includes

- reduce compile time by a little bit (full-core: ~0.7s for me)
- thanks to 'include-what-you-use' for some help
- include Standard C header files before any other (coding style)

1 files changed, 0 insertions, 2 deletions

diff --git a/src/etc.c b/src/etc.c
index 82394891f..8d19a1eab 100644
--- a/src/etc.c
+++ b/src/etc.c
@@ -6,8 +6,6 @@
 
 #include "mruby.h"
 #include "mruby/string.h"
-#include "error.h"
-#include "mruby/numeric.h"
 #include "mruby/data.h"
 #include "mruby/class.h"