Hi,

What you can do is that you can set default value for the specified field. Suppose if your customers are more from US, in the country field just set it as the default value, so that you don't need to choose it all the time.

See this video and see how to set default value for a field from user interface in developer mode: How To Set Default Value For A Field in Odoo 

Rather than looking to delete countries you can try the above method or just keep those countries as inactive by setting active as False if possible.

Thanks

Thank you both for your response.   I was able to set the default country on the contact forms. 

Could you tell me specifically where I can see a list of countries so I could set them as inactive?

country_id = field.char(default='name country')in the table "res_country_state"