wrapper.c: remove unused gitmkstemps() function

The last call to the mkstemps() function was removed in commit 659488326
("wrapper.c: delete dead function git_mkstemps()", 22-04-2016). In order
to support platforms without mkstemps(), this functionality was provided,
along with a Makefile build variable (NO_MKSTEMPS), by the gitmkstemps()
function. Remove the dead code, along with the defunct build machinery.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -639,11 +639,6 @@ extern int gitsetenv(const char *, const char *, int);
 extern char *gitmkdtemp(char *);
 #endif
 
-#ifdef NO_MKSTEMPS
-#define mkstemps gitmkstemps
-extern int gitmkstemps(char *, int);
-#endif
-
 #ifdef NO_UNSETENV
 #define unsetenv gitunsetenv
 extern void gitunsetenv(const char *);