remove unneeded app context

[peterlada]

thus preventing flask from destroying the db session when used with sqlalchemy in single session mode for testing.

[codecov[bot]]

Codecov Report

Merging #92 into master will decrease coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   97.94%   97.93%   -0.01%     
==========================================
  Files           6        6              
  Lines         292      291       -1     
  Branches       25       25              
==========================================
- Hits          286      285       -1     
  Misses          4        4              
  Partials        2        2

Impacted Files	Coverage Δ
src/flask_rq2/job.py	100% <100%> (ø)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 58eedf6...03efac8. Read the comment docs.