[clang] Remove stdint.h include from a test

Tests must not include headers from the host system.
It looks like the include wasn't needed for anything, so just remove it.

This makes check-clang work in a `git bash` launched from a cmd.exe
that isn't an MSVC shell (that is, %INCLUDE% isn't set).

clang/test/Index/retain-excluded-conditional-blocks.m

@@ -1,9 +1,5 @@
 // RUN: c-index-test -retain-excluded-conditional-blocks %s | FileCheck %s
 
-#include <stdint.h>
-
-// CHECK: TypedefDecl=intptr_t
-
 // CHECK: [[@LINE+1]]:12: ObjCInterfaceDecl=MyCls
 @interface MyCls
 // CHECK: [[@LINE+1]]:8: ObjCInstanceMethodDecl=some_meth