Remove covid_therapeutics_raw table

[evansd]

The original table here:
https://docs.opensafely.org/ehrql/reference/schemas/raw.tpp/#covid_therapeutics_raw

Has been supplanted by the cleaned version here:
https://docs.opensafely.org/ehrql/reference/schemas/tpp/#covid_therapeutics

And we don't want to maintain the raw version longer than we have to.

Technically, this is a breaking change. But I believe that this table only had one user, and that user has since migrated to the cleaned version:
https://github.com/search?q=org%3Aopensafely+covid_therapeutics_raw+AND+NOT+path%3A.devcontainer&type=code

So it should be fine to remove that table in a feat: commit.

Slack thread:
https://bennettoxford.slack.com/archives/C31D62X5X/p1716557336906049?thread_ts=1715159270.056439&cid=C31D62X5X