configure: Drop test for fork()

fork() is never used conditionally.

configure

@@ -1627,7 +1627,6 @@ SYSTEM_FUNCS="
     CommandLineToArgvW
     CryptGenRandom
     fcntl
-    fork
     getaddrinfo
     gethrtime
     getopt
@@ -4617,7 +4616,6 @@ check_cpp_condition unistd.h "defined(_POSIX_MONOTONIC_CLOCK)" &&
       check_lib clock_gettime time.h clock_gettime -lrt; }
 
 check_func  fcntl
-check_func  fork
 check_func  gethrtime
 check_func  getopt
 check_func  getrusage