syncobj.h no longer defines shared_guard, so remove those define's

The removed preprocessor macro's refer to types that are not defined in
the file anymore; the only other place where shared_guard is defined is
in winobj.h, which also defines the same macro's. Therefore, this change
is safe.

(Side note is that these macro's weren't used at all anyway, but that is
orthogonal to the issue.)

contrib/epee/include/syncobj.h

@@ -150,9 +150,6 @@ namespace epee
   };
 
 
-#define  SHARED_CRITICAL_REGION_BEGIN(x) { shared_guard   critical_region_var(x)
-#define  EXCLUSIVE_CRITICAL_REGION_BEGIN(x) { exclusive_guard   critical_region_var(x)
-
 #define  CRITICAL_REGION_LOCAL(x) {boost::this_thread::sleep_for(boost::chrono::milliseconds(epee::debug::g_test_dbg_lock_sleep()));}   epee::critical_region_t<decltype(x)>   critical_region_var(x)
 #define  CRITICAL_REGION_BEGIN(x) { boost::this_thread::sleep_for(boost::chrono::milliseconds(epee::debug::g_test_dbg_lock_sleep())); epee::critical_region_t<decltype(x)>   critical_region_var(x)
 #define  CRITICAL_REGION_LOCAL1(x) {boost::this_thread::sleep_for(boost::chrono::milliseconds(epee::debug::g_test_dbg_lock_sleep()));} epee::critical_region_t<decltype(x)>   critical_region_var1(x)