Revert "Omnibus to implement CFRunLoop with kevent. (#3004)"

This reverts commit 5f57e70.

Author: compnerd

CoreFoundation/Base.subproj/CFPlatform.c

@@ -249,11 +249,7 @@ const char *_CFProcessPath(void) {
 
 #if TARGET_OS_MAC || TARGET_OS_WIN32 || TARGET_OS_BSD
 CF_CROSS_PLATFORM_EXPORT Boolean _CFIsMainThread(void) {
-#if defined(__OpenBSD__)
-    return pthread_equal(pthread_self(), _CFMainPThread) != 0;
-#else
     return pthread_main_np() == 1;
-#endif
 }
 #endif
 
@@ -778,7 +774,7 @@ static void __CFTSDFinalize(void *arg) {
 #if TARGET_OS_WASI
     __CFMainThreadHasExited = true;
 #else
-    if (_CFIsMainThread()) {
+    if (pthread_main_np() == 1) {
         // Important: we need to be sure that the only time we set this flag to true is when we actually can guarentee we ARE the main thread. 
         __CFMainThreadHasExited = true;
     }