Remove ServerRequest environment

[Baptouuuu]

At first it was there to mimic psr messages. But when used with innmind/http-server or innmind/framework it feels awkward to have env variables accessible on the request as it doesn't change between 2 requests.

Also env variables should be used to initialize an app and not used afterward.

So to push toward a better usage, env variables will be provided by innmind/http-server.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.05%. Comparing base (be66a37) to head (bc7b33f).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #23      +/-   ##
=============================================
- Coverage      94.07%   94.05%   -0.03%     
+ Complexity      1096     1075      -21     
=============================================
  Files            197      192       -5     
  Lines           4323     4236      -87     
=============================================
- Hits            4067     3984      -83     
+ Misses           256      252       -4     

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