Incorrect `TOR_V2_AUTH_COOKIE_REGEX` regular expression when validating config

[eloquence]

This was reported as an informational finding in the 2020 SecureDrop Workstation audit (TOB-SDW-001):

The TOR_V2_AUTH_COOKIE_REGEX regular expression for validating Tor's v2 auth cookie has an "A-z" character range specified in its character set. This range overlaps with the "a-z" range used in the same character set and also includes characters between the letters "Z" and "a," which are outside of the Tor v2 auth cookie format: "[\]^_ ."`

[eloquence]

Note that v2 onion services will no longer be supported by SecureDrop after April 30, 2021, which is a little over a month away, so preparing a PR to remove v2 support may be the pragmatic way to resolve this issue.

[eloquence]

This was resolved a while ago via #694.