chore: Complete removal of ProjectTemplate models

[markstory]

Remove the columns and tables for real

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1045_projecttemplate_cleanup.py

for 1045_projecttemplate_cleanup in sentry

--
-- Remove field template from project
--
ALTER TABLE "sentry_project" DROP COLUMN "template_id" CASCADE;
--
-- Delete model ProjectTemplateOption
--
DROP TABLE "sentry_projecttemplateoption" CASCADE;
--
-- Delete model ProjectTemplate
--
DROP TABLE "sentry_projecttemplate" CASCADE;

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1046_projecttemplate_cleanup.py

for 1046_projecttemplate_cleanup in sentry

--
-- Remove field template from project
--
ALTER TABLE "sentry_project" DROP COLUMN "template_id" CASCADE;
--
-- Delete model ProjectTemplateOption
--
DROP TABLE "sentry_projecttemplateoption" CASCADE;
--
-- Delete model ProjectTemplate
--
DROP TABLE "sentry_projecttemplate" CASCADE;