ICU-20729 Remove obsolete U_HAVE_STD_ATOMICS and similar @internal macros.
diff --git a/icu4c/source/common/putilimp.h b/icu4c/source/common/putilimp.h
index 73defd9..d9c90cf 100644
--- a/icu4c/source/common/putilimp.h
+++ b/icu4c/source/common/putilimp.h
@@ -179,76 +179,6 @@
/** @} */
/*===========================================================================*/
-/** @{ GCC built in functions for atomic memory operations */
-/*===========================================================================*/
-
-/**
- * \def U_HAVE_GCC_ATOMICS
- * @internal
- */
-#ifdef U_HAVE_GCC_ATOMICS
- /* Use the predefined value. */
-#elif U_PLATFORM == U_PF_MINGW
- #define U_HAVE_GCC_ATOMICS 0
-#elif U_GCC_MAJOR_MINOR >= 404 || defined(__clang__)
- /* TODO: Intel icc and IBM xlc on AIX also support gcc atomics. (Intel originated them.)
- * Add them for these compilers.
- * Note: Clang sets __GNUC__ defines for version 4.2, so misses the 4.4 test here.
- */
-# define U_HAVE_GCC_ATOMICS 1
-#else
-# define U_HAVE_GCC_ATOMICS 0
-#endif
-
-/** @} */
-
-/**
- * \def U_HAVE_STD_ATOMICS
- * Defines whether to use the C++11 std::atomic functions.
- * If false, ICU will fall back to compiler or platform specific alternatives.
- * Note: support for these fall back options for atomics will be removed in a future version
- * of ICU, and the use of C++ 11 atomics will be required.
- * @internal
- */
-#ifdef U_HAVE_STD_ATOMICS
- /* Use the predefined value. */
-#else
-# define U_HAVE_STD_ATOMICS 1
-#endif
-
-/**
- * \def U_HAVE_CLANG_ATOMICS
- * Defines whether Clang c11 style built-in atomics are available.
- * These are used in preference to gcc atomics when both are available.
- */
-#ifdef U_HAVE_CLANG_ATOMICS
- /* Use the predefined value. */
-#elif __has_builtin(__c11_atomic_load) && \
- __has_builtin(__c11_atomic_store) && \
- __has_builtin(__c11_atomic_fetch_add) && \
- __has_builtin(__c11_atomic_fetch_sub)
-# define U_HAVE_CLANG_ATOMICS 1
-#else
-# define U_HAVE_CLANG_ATOMICS 0
-#endif
-
-
-/**
- * \def U_HAVE_STD_MUTEX
- * Defines whether to use the C++11 std::mutex functions.
- * If false, ICU will fall back to compiler or platform specific alternatives.
- * std::mutex is preferred, and used by default unless this setting is overridden.
- * Note: support for other options for mutexes will be removed in a future version
- * of ICU, and the use of std::mutex will be required.
- * @internal
- */
-#ifdef U_HAVE_STD_MUTEX
- /* Use the predefined value. */
-#else
-# define U_HAVE_STD_MUTEX 1
-#endif
-
-/*===========================================================================*/
/** @{ Programs used by ICU code */
/*===========================================================================*/
