Remove useless pointer update in StatsShmemInit()

Remove useless pointer update in StatsShmemInit()

This pointer was not used after its last update.  This variable
assignment was most likely a vestige artifact of the earlier versions of
the patch set that have led to 5891c7a8ed8f.

This pointer update is useless, so let's remove it.  It removes one call
to pgstat_dsa_init_size(), making the code slightly easier to grasp.

Author: Bertrand Drouvot <[email protected]>
Discussion: https://postgr.es/m/[email protected]