Revert "Use "transient" files for blind writes, take 2".

This reverts commit fba105b109.
That approach had problems with the smgr-level state not tracking what
we really want to happen, and with the VFD-level state not tracking the
smgr-level state very well either.  In consequence, it was still possible
to hold kernel file descriptors open for long-gone tables (as in recent
report from Tore Halset), and yet there were also cases of FDs being closed
undesirably soon.  A replacement implementation will follow.

src/include/storage/fd.h

@@ -66,7 +66,6 @@ extern int	max_safe_fds;
 /* Operations on virtual Files --- equivalent to Unix kernel file ops */
 extern File PathNameOpenFile(FileName fileName, int fileFlags, int fileMode);
 extern File OpenTemporaryFile(bool interXact);
-extern void FileSetTransient(File file);
 extern void FileClose(File file);
 extern int	FilePrefetch(File file, off_t offset, int amount);
 extern int	FileRead(File file, char *buffer, int amount);

src/include/storage/smgr.h

@@ -60,7 +60,6 @@ typedef struct SMgrRelationData
 	 * submodules.	Do not touch them from elsewhere.
 	 */
 	int			smgr_which;		/* storage manager selector */
-	bool		smgr_transient; /* T if files are to be closed at EOXact */
 
 	/* for md.c; NULL for forks that are not open */
 	struct _MdfdVec *md_fd[MAX_FORKNUM + 1];
@@ -73,7 +72,6 @@ typedef SMgrRelationData *SMgrRelation;
 
 extern void smgrinit(void);
 extern SMgrRelation smgropen(RelFileNode rnode, BackendId backend);
-extern void smgrsettransient(SMgrRelation reln);
 extern bool smgrexists(SMgrRelation reln, ForkNumber forknum);
 extern void smgrsetowner(SMgrRelation *owner, SMgrRelation reln);
 extern void smgrclose(SMgrRelation reln);