launch_backend: Remove duplicate include under EXEC_BACKEND

Hi,

While reviewing another patch, I noticed that launch_backend.c includes storage/pg_shmem.h twice: once in the common include section, and again inside an #ifdef EXEC_BACKEND block.

I first tried removing the earlier include, but that led to a build failure. So instead, I removed the duplicate include inside the #ifdef EXEC_BACKEND block.

I have verified a normal build and “PROFILE=‘-DEXEC_BACKEND’ make”, both passed.

Since I was already touching this area, I also combined the two adjacent #ifdef EXEC_BACKEND blocks into one.

Please see the attached patch for details.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/