fix: remove MIDWAY_SERVER_ENV default value

[czy88840616]

No description provided.

[gitpod-io]

[codecov-io]

Codecov Report

Merging #966 (0194520) into 2.x (5afdfca) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              2.x     #966      +/-   ##
==========================================
- Coverage   86.40%   86.39%   -0.01%     
==========================================
  Files         204      204              
  Lines        7978     7977       -1     
  Branches     1587     1586       -1     
==========================================
- Hits         6893     6892       -1     
  Misses       1038     1038              
  Partials       47       47              

Impacted Files	Coverage Δ
...ackages-serverless/serverless-app/src/framework.ts	63.44% <ø> (-0.20%)	⬇️

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