In Salesforce.com, if there are fields with a blue dot in page layout of an object (as shown below), you can’t remove them from the page out. For example the ‘Parent Account’ field in Account object cannot be removed from the Page Layout.

Fields with Blue Dot in Page Layout

The workaround to hide this field from the users is to edit the Profile of the user and revoke the ‘Read’ access from that field under field level permission of that object. Once done, the field will not be visible to the users of that profile.