Remove Read-Only lock from SharePoint 2013/2016 site collection
Set/Remove Read-Only lock from SharePoint 2013/2016 site collection using PowerShell:
$siteUrl = "https://mysiteurl"
#mark site as not locked
$s = get-spsite $siteUrl
$s.WriteLocked = $false
set-spsite $siteUrl -LockState Unlock
$s.Archived = $false
#mark site as read-only
set-spsite $siteUrl -LockState ReadOnly