revert unwanted and inadvertent change that slipped into mmap.c

commit ae388becb529428ac926da102f1d025b3c3968da accidentally
introduced #define SYSCALL_NO_TLS 1 in mmap.c, which was probably a
stale change left around from unrelated syscall timing measurements.
reverse it.

src/mman/mmap.c

@@ -1,4 +1,3 @@
-#define SYSCALL_NO_TLS 1
 #include <unistd.h>
 #include <sys/mman.h>
 #include <errno.h>