mingw: remove duplicate `USE_NED_ALLOCATOR` directive

nedalloc was added to fix the slowness of memory allocator. Here
specifically for the MSys2 build there seems to be a duplication of
USE_NED_ALLOCATOR directive. So this patch intends to remove the
duplicate USE_NED_ALLOCATOR and keeping it only into the MSys2 config
section so it still uses the nedalloc.

Signed-off-by: Harshil-Jani <harshiljani2002@gmail.com>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.uname

@@ -652,7 +652,6 @@ ifeq ($(uname_S),MINGW)
 	USE_WIN32_IPC = YesPlease
 	USE_WIN32_MMAP = YesPlease
 	MMAP_PREVENTS_DELETE = UnfortunatelyYes
-	USE_NED_ALLOCATOR = YesPlease
 	UNRELIABLE_FSTAT = UnfortunatelyYes
 	OBJECT_CREATION_USES_RENAMES = UnfortunatelyNeedsTo
 	NO_REGEX = YesPlease