pkp/pkp-lib#10977 Fix issues within merge user functionality

[taslangraham]

For #10977

[Hafsa-Naeem]

pluck(...)->toArray() loads all matching email_log_id values into PHP memory before running the update. and might not be optimal for large datasets. how about using?

->whereNotIn('email_log_id', function ($sub) use ($newUserId, $oldUserId) {
    $sub->select('t1.email_log_id')
        ->from(DB::raw('email_log_users as t1'))
        ->join(DB::raw('email_log_users as t2'), 't1.email_log_id', '=', 't2.email_log_id')
        ->where('t1.user_id', $newUserId)
        ->where('t2.user_id', $oldUserId);
})

[taslangraham]

@Hafsa-Naeem Thanks for the review.
The suggested query produced an error - General error: 1093 You can't specify target table 'email_log_users' for update in FROM clause so I had to tweak it a bit. Please take a look

[Hafsa-Naeem]

@taslangraham Looks good to me.