extmod/moduplatform: Remove _M_IX86 test for xtensa.

Since _M_IX86 is already being checked in the x86 case, it will never
be true in the xtensa case and can be removed.

Signed-off-by: David Lechner <david@pybricks.com>

extmod/moduplatform.h

@@ -41,7 +41,7 @@
 #define MICROPY_PLATFORM_ARCH   "x86_64"
 #elif defined(__i386__) || defined(_M_IX86)
 #define MICROPY_PLATFORM_ARCH   "x86"
-#elif defined(__xtensa__) || defined(_M_IX86)
+#elif defined(__xtensa__)
 #define MICROPY_PLATFORM_ARCH   "xtensa"
 #else
 #define MICROPY_PLATFORM_ARCH   ""