Revert "Consistently test for in-use shared memory."

This reverts commits 2f932f71d9,
16ee6eaf80 and
6f0e190056.  The buildfarm has revealed
several bugs.  Back-patch like the original commits.

Discussion: https://postgr.es/m/20190404145319.GA1720877@rfd.leadboat.com

src/backend/port/win32_shmem.c

@@ -109,9 +109,14 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
  *
  * Create a shared memory segment of the given size and initialize its
  * standard header.
+ *
+ * makePrivate means to always create a new segment, rather than attach to
+ * or recycle any existing segment. On win32, we always create a new segment,
+ * since there is no need for recycling (segments go away automatically
+ * when the last backend exits)
  */
 PGShmemHeader *
-PGSharedMemoryCreate(Size size, int port,
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
 					 PGShmemHeader **shim)
 {
 	void	   *memAddress;