[ATFE] Remove Downstream Change arm#378

With the merging of llvm/llvm-project#147956 upstream,
the downstream patch is not required anymore.

Author: simpal01

libcxx/include/__configuration/platform.h

@@ -49,11 +49,6 @@
 #  include <picolibc.h>
 #endif
 
-// Downstream issue: 378 (Include newlib.h to define _NEWLIB_VERSION)
-#if __has_include(<newlib.h>)
-#  include <newlib.h>
-#endif
-
 #ifndef __BYTE_ORDER__
 #  error                                                                                                               \
       "Your compiler doesn't seem to define __BYTE_ORDER__, which is required by libc++ to know the endianness of your target platform"