config.mak.uname: remove SPARSE_FLAGS setting for cygwin

Since commit f66450ae9 ("cygwin: Remove the Win32 l/stat() implementation", 2013-06-22), the cygwin build has not used the WIN32 API/header files. This means that the '-isystem /usr/include/w32api' option to sparse is no longer necessary (to allow sparse to find the WIN32 header files). In addition, the '-Wno-one-bit-signed-bitfield' option can be removed, since the warning suppressed by that option was only provoked by a WIN32 header file. Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>