compat/w32pthreads: drop the cancellation stubs

0830e9116f added pthread_setcancelstate() and the PTHREAD_CANCEL_*
values for the udp receive thread, which is no longer cancelled and
does not call them. No other file refers to them.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

compat/w32pthreads.h

@@ -63,9 +63,6 @@ typedef CONDITION_VARIABLE pthread_cond_t;
 #define InitializeCriticalSection(x) InitializeCriticalSectionEx(x, 0, 0)
 #define WaitForSingleObject(a, b) WaitForSingleObjectEx(a, b, FALSE)
 
-#define PTHREAD_CANCEL_ENABLE 1
-#define PTHREAD_CANCEL_DISABLE 0
-
 #if HAVE_WINRT
 #define THREADFUNC_RETTYPE DWORD
 #else
@@ -210,11 +207,6 @@ static inline int pthread_cond_signal(pthread_cond_t *cond)
     return 0;
 }
 
-static inline int pthread_setcancelstate(int state, int *oldstate)
-{
-    return 0;
-}
-
 static inline int win32_thread_setname(const char *name)
 {
 #if !HAVE_UWP