fix building the core with --disable-unicode

I changed some bytearray methods to use strings instead of unicode like bytes_repr
Also, bytearray.fromhex() can take strings as well as unicode
diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c
index 4f2e53f..5cf5bad 100644
--- a/Python/formatter_unicode.c
+++ b/Python/formatter_unicode.c
@@ -2,6 +2,9 @@
    built-in formatter for unicode.  That is, unicode.__format__(). */
 
 #include "Python.h"
+
+#ifdef Py_USING_UNICODE
+
 #include "../Objects/stringlib/unicodedefs.h"
 
 #define FORMAT_STRING _PyUnicode_FormatAdvanced
@@ -11,3 +14,5 @@
    will convert them to unicode. */
 
 #include "../Objects/stringlib/formatter.h"
+
+#endif