patch 8.1.0983: checking __CYGWIN32__ unnecessarily

Problem:    Checking __CYGWIN32__ unnecessarily.
Solution:   Remove the checks. (Ken Takata)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7f50555..0ad8d84 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -6155,7 +6155,7 @@
 #ifdef MSWIN
 	"win32",
 #endif
-#if defined(UNIX) && (defined(__CYGWIN32__) || defined(__CYGWIN__))
+#if defined(UNIX) && defined(__CYGWIN__)
 	"win32unix",
 #endif
 #ifdef _WIN64