ksh [emacs.c] -- simplify isu8cont()

[ropers]

Index: emacs.c
===================================================================
RCS file: /cvs/src/bin/ksh/emacs.c,v
retrieving revision 1.87
diff -u -r1.87 emacs.c
--- emacs.c     8 May 2020 14:30:42 -0000       1.87
+++ emacs.c     25 Jul 2020 16:31:22 -0000
@@ -269,10 +269,11 @@
        { 0, 0, 0 },
 };

+/* is octet a UTF-8 continuation byte? */
 int
 isu8cont(unsigned char c)
 {
-       return (c & (0x80 | 0x40)) == 0x80;
+       return (c & 0xC0) == 0x80;
 }

 int