Prefer the pthread types from CDispatch

The types `pthread_mutex_t` and `pthread_cond_t` were defined via both
`SwiftGlibc` and `CDistpatch` but a clang fix should merge these decls
and consider `CDispatch` as the true origin.

rdar://84677782

Author: xymus

Sources/Foundation/NSLock.swift

@@ -22,11 +22,6 @@ public protocol NSLocking {
     func unlock()
 }
 
-#if canImport(Glibc)
-typealias pthread_mutex_t = Glibc.pthread_mutex_t
-typealias pthread_cond_t = Glibc.pthread_cond_t
-#endif
-
 #if os(Windows)
 private typealias _MutexPointer = UnsafeMutablePointer<SRWLOCK>
 private typealias _RecursiveMutexPointer = UnsafeMutablePointer<CRITICAL_SECTION>