How to delete "In code" views? Some Drupal views I have are "In code" (while some others are "In database"); I understand that some are hard-coded in some PHP files and some are coded in the SQL.

Generally, what are the PHP files in which the "In code" views are stored?
The file name convention for default views provided by a module uses the extension .views_default.inc. 

Alternatively, if a module isn't using standard naming conventions, you can search the code base for hook_views_default_views_alter() implementations (e.g. grep -r '_views_default_views_alter' . ) to find these views.