Revert token authentication 5.x

[chrisminett]

Revert the token authentication changes added in #18 , keeping the deprecation for getConfig().

Although this is essentially a BC break as it removes code, no implementation can have used token auth as it is not live in the Maxemail app.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.86%. Comparing base (f105360) to head (042ecb7).
Report is 3 commits behind head on 5.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                5.x      #20      +/-   ##
============================================
- Coverage     86.07%   85.86%   -0.21%     
+ Complexity       77       75       -2     
============================================
  Files             5        5              
  Lines           280      276       -4     
============================================
- Hits            241      237       -4     
  Misses           39       39              

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[chrisminett]

Checking that the token auth code has been correctly reverted:

• Compare this branch to immediately before Token authentication #18 , showing only the changes to deprecate getConfig(): 5a5e665...revert-token-auth-5
• Compare this branch to the next commit, which deprecated getConfig(), showing that the only diff is the labelling changes: 386e78e...revert-token-auth-5