Remove accidental change committed in r274403.

llvm-svn: 274407
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: d3ac6ae7d337ae96f1e65c4a5dca06c59ae99f45
diff --git a/src/chrono.cpp b/src/chrono.cpp
index 14b848b..266eed8 100644
--- a/src/chrono.cpp
+++ b/src/chrono.cpp
@@ -6,7 +6,7 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-#define _LIBCPP_BUILDING_CHRONO
+
 #include "chrono"
 #include "cerrno"        // errno
 #include "system_error"  // __throw_system_error