Clears any currently stored token. The next time bigrquery needs a token, the
token acquisition process starts over, with a fresh call to bq_auth()
and,
therefore, internally, a call to gargle::token_fetch()
. Unlike some other
packages that use gargle, bigrquery is not usable in a de-authorized state.
Therefore, calling bq_deauth()
only clears the token, i.e. it does NOT
imply that subsequent requests are made with an API key in lieu of a token.