The Montgomery County Democratic Committee Thursday night endorsed its two candidates for county commissioner.   State Representative Josh Shapiro and Whitemarsh Township Supervisor Leslie Richards will lead the ticket into the upcoming election campaign.   Their names were put into nomination by current Commissioner Joe Hoeffel.   Shapiro thanked him for stepping aside in the interest of party unity.   Other candidates winning the endorsement of the Democratic Committee include incumbent Controller Diane Morgan and sheriff candidate William Holt.   Incumbent Clerk of Courts Ann Thornburg Weiss as well as recorder of deeds candidate Linda Hee also received an endorsement from the party organization.