[Bug #19967] Revert "configure.ac: LIBPATHENV on macOS"

This reverts commit 1961c786aa.  These
environment variables should no longer propagate to child processes.

configure.ac

@@ -3086,7 +3086,7 @@ AC_SUBST(EXTOBJS)
 	[darwin*], [	: ${LDSHARED='$(CC) -dynamic -bundle'}
 			: ${DLDSHARED='$(CC) -dynamiclib'}
 			: ${LDFLAGS=""}
-			: ${LIBPATHENV=DYLD_FALLBACK_LIBRARY_PATH}
+			: ${LIBPATHENV=DYLD_LIBRARY_PATH}
 			: ${PRELOADENV=DYLD_INSERT_LIBRARIES}
                         AS_IF([test x"$enable_shared" = xyes], [
                             # Resolve symbols from libruby.dylib in $(LIBS) when --enable-shared