Remove the nxt_getpid() alias.

Since the previous commit, nxt_getpid() is only ever aliased to
getpid(2).

nxt_getpid() was only used once in the code, while there are multiple
direct uses of getpid(2)

  $ grep -r "getpid()" src/
  src/nxt_unit.c:    nxt_unit_pid = getpid();
  src/nxt_process.c:    nxt_pid = nxt_getpid();
  src/nxt_process.c:    nxt_pid = getpid();
  src/nxt_lib.c:    nxt_pid = getpid();
  src/nxt_process.h:#define nxt_getpid()                                                          \
  src/nxt_process.h:#define nxt_getpid()                                                          \
  src/nxt_process.h:    getpid()

Just remove it and convert the _single_ instance of nxt_getpid() to
getpid(2).

Reviewed-by: Alejandro Colomar <[email protected]>
Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000

src/nxt_process.c

@@ -269,7 +269,7 @@ nxt_process_child_fixup(nxt_task_t *task, nxt_process_t *process)
 
     nxt_ppid = nxt_pid;
 
-    nxt_pid = nxt_getpid();
+    nxt_pid = getpid();
 
     process->pid = nxt_pid;
     process->isolated_pid = nxt_pid;

src/nxt_process.h

@@ -13,9 +13,6 @@
 #endif
 
 
-#define nxt_getpid()                                                          \
-    getpid()
-
 typedef pid_t            nxt_pid_t;