Remove mimetype check

[Jacob-Eliat-Eliat]

Seems like uploading a file through fusion with .ndjson extension will automatically set some different mimetype. Let's just remove this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.25%. Comparing base (d1e22af) to head (fab94ee).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #989      +/-   ##
==========================================
- Coverage   83.26%   83.25%   -0.01%     
==========================================
  Files          47       47              
  Lines        3143     3142       -1     
  Branches      471      470       -1     
==========================================
- Hits         2617     2616       -1     
  Misses        526      526              

Files with missing lines	Coverage Δ
...n/scala/cognite/spark/v1/FileContentRelation.scala	93.33% <ø> (-0.42%)	⬇️