[libc++][NFC] Fix copy-paste errors in tests

The test precision_type.pass.cpp was a duplicate of precision.pass.cpp,
so it is removed. atomic_flag_test.pass.cpp was a duplicate of
atomic_flag_test_and_set.pass.cpp, so instead I wrote a proper
test for it. Those duplicate tests were detected with

     find libcxx ! -empty -type f -exec md5sum {} + | sort | uniq -w32 -dD

Author: ldionne

libcxx/test/std/atomics/atomics.flag/atomic_flag_test.pass.cpp

@@ -12,8 +12,8 @@
 
 // struct atomic_flag
 
-// bool atomic_flag_test_and_set(volatile atomic_flag*);
-// bool atomic_flag_test_and_set(atomic_flag*);
+// bool atomic_flag_test(const volatile atomic_flag*);
+// bool atomic_flag_test(const atomic_flag*);
 
 #include <atomic>
 #include <cassert>
@@ -25,15 +25,17 @@ int main(int, char**)
     {
         std::atomic_flag f;
         f.clear();
-        assert(atomic_flag_test_and_set(&f) == 0);
-        assert(f.test_and_set() == 1);
+        assert(atomic_flag_test(&f) == 0);
+        assert(f.test_and_set() == 0);
+        assert(atomic_flag_test(&f) == 1);
     }
     {
         volatile std::atomic_flag f;
         f.clear();
-        assert(atomic_flag_test_and_set(&f) == 0);
-        assert(f.test_and_set() == 1);
+        assert(atomic_flag_test(&f) == 0);
+        assert(f.test_and_set() == 0);
+        assert(atomic_flag_test(&f) == 1);
     }
 
-  return 0;
+    return 0;
 }

libcxx/test/std/atomics/atomics.flag/atomic_flag_test_explicit.pass.cpp

@@ -111,5 +111,5 @@ int main(int, char**)
         assert(atomic_flag_test_explicit(&f, std::memory_order_seq_cst) == 1);
     }
 
-  return 0;
+    return 0;
 }

libcxx/test/std/utilities/time/time.hms/time.hms.members/precision.pass.cpp

@@ -44,7 +44,7 @@ constexpr unsigned long long powers[] = {
 	100000000000000000ULL,
 	1000000000000000000ULL,
 	10000000000000000000ULL
-	};
+};
 
 template <typename Duration, unsigned width>
 constexpr bool check_precision()