cygwin: stop forcing core.filemode=false

We force core.filemode=false since c869753e (Force core.filemode to
false on Cygwin., 2006-12-30), even when the repository is on a
filesystem on which Cygwin can give us trustable filemodes, because
many native Windows applications the users use to edit files in the
working tree tend to (re)create files with executable bit randomly
set or reset.  However, binary distribution of Git that is supplied
by the downstream project to its users has been built without this
consideration.

Drop NO_TRUSTABLE_FILEMODE from our default configuration so that
hand-compiled Git out of box will match theirs.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.uname

@@ -169,7 +169,6 @@ ifeq ($(uname_O),Cygwin)
 	endif
 	NEEDS_LIBICONV = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
-	NO_TRUSTABLE_FILEMODE = UnfortunatelyYes
 	NO_ST_BLOCKS_IN_STRUCT_STAT = YesPlease
 	X = .exe
 	COMPAT_OBJS += compat/cygwin.o