It looks like you have to make this change in modules/Opportunities/metadata/editviewdefs.php (or possibly in custom/modules/Opportunities/metadata/editviewdefs.php).
Change:
PHP Code:
array (
'account_name',
array( 'name'=>'amount','displayParams'=>array('required'=>true)),
),
array (
'opportunity_type',
array('name'=>'date_closed', 'displayParams'=>array('required'=>true)),
),
to this - which removes the "required" attribute for the two fields in question.
PHP Code:
array (
'account_name', 'amount',
),
array (
'opportunity_type', 'date_closed',
),
Bookmarks