Rename test_stale_deps to test_unused_deps

[lgoettgens]

Resolves #264.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.20%. Comparing base (b51f800) to head (9ed85ba).
⚠️ Report is 57 commits behind head on master.

Files with missing lines	Patch %	Lines
src/unused_deps.jl	86.66%	2 Missing ⚠️
src/Aqua.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #270   +/-   ##
=======================================
  Coverage   75.20%   75.20%           
=======================================
  Files          11       11           
  Lines         750      750           
=======================================
  Hits          564      564           
  Misses        186      186           

Flag	Coverage Δ
unittests	75.20% <83.33%> (ø)

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[hyrodium]

Do we have a plan to release v0.9? (x-ref: #229)
I thought it would be nice if the next breaking release is v1.0.0.