util: drop const_int_one/const_int_zero again

There's only a single user remaining now that we have setsockopt_int(),
let's define those variables locally.

This more or less reverts 6d5e65f645.

src/basic/util.c

@@ -51,9 +51,6 @@ int saved_argc = 0;
 char **saved_argv = NULL;
 static int saved_in_initrd = -1;
 
-const int const_int_zero = 0;
-const int const_int_one = 1;
-
 size_t page_size(void) {
         static thread_local size_t pgsz = 0;
         long r;

src/basic/util.h

@@ -232,6 +232,3 @@ int version(void);
 int str_verscmp(const char *s1, const char *s2);
 
 void disable_coredumps(void);
-
-extern const int const_int_zero;
-extern const int const_int_one;