xslate: don't try to remove cache dir

[haarg]

On older deployments, the xslate cache would sometimes not correctly
detect new template files, leading to unpredictable errors. Purging of
the cache directory on startup was added to deal with this.

The normal deployment is now done with a docker container, so there is
nothing to clear out at startup. Additionally, the cache directory isn't
being configured to a static path, so it will always be using a newly
created temp directory. Clearing out the template cache is no longer
relevant, so it can be removed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.36%. Comparing base (29f566b) to head (ec54730).
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3366      +/-   ##
==========================================
- Coverage   73.41%   73.36%   -0.06%     
==========================================
  Files          68       68              
  Lines        2389     2388       -1     
  Branches      335      335              
==========================================
- Hits         1754     1752       -2     
- Misses        507      508       +1     
  Partials      128      128              

Files with missing lines	Coverage Δ
lib/MetaCPAN/Web/View/Xslate.pm	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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