Fix file deletion command in recovery_1st_stage.sample.

Fix  file deletion command in recovery_1st_stage.sample.

In the recovery_1st_stage script, the file deletion command has been modified.
Previously, files under ARCHIVEDIR were deleted using "rm *", but when the total size of the target files exceeded ARG_MAX, it resulted in an "Argument list too long" error and caused the recovery_1st_stage script to fail.
By switching to the find command to delete files one by one, this error is avoided.

Discussion: https://github.com/pgpool/pgpool2/issues/94
Backpatch-through: v4.2