Script to remove Exchange 2010 AutoMapping for all mailboxes

That is incredibly easy. You simply need to retrieve a list of mailboxes and run the example against each of them:

# Get all mailboxes in the forest
$Mailboxes = Get-Mailbox -ResultSize unlimited -IgnoreDefaultScope
$ConfirmPreference = 'None'

# Iterate over each mailbox
foreach($Mailbox in $Mailboxes)
{
    try 
    {
        # Try to run the example fix against the current $Mailbox
        $FixAutoMapping = Get-MailboxPermission $Mailbox |where {$_.AccessRights -eq "FullAccess" -and $_.IsInherited -eq $false}
        $FixAutoMapping | Remove-MailboxPermission
        $FixAutoMapping | ForEach {Add-MailboxPermission -Identity $_.Identity -User $_.User -AccessRights:FullAccess -AutoMapping $false} 
    }
    catch
    {
        # Inform about the error if unsuccessful
        Write-Host "Encountered error: $($Error[0].Exception) on mailbox $($Mailbox.DisplayName)" -ForegroundColor Red
    }
}