Revert use of ContextVariablesX.jl

[omus]

Reverts the changes from #91 which introduced the use of ContextVariablesX.jl. Unfortunately this package doesn't work as expected when the logger is changed resulting in unexpected breakage. I've included the tests from #91 here.

Fixes #92. Re-opens #89.

[codecov]

Codecov Report

Merging #93 (791ecf8) into master (4572de4) will increase coverage by 0.40%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   83.72%   84.12%   +0.40%     
==========================================
  Files           6        6              
  Lines         129      126       -3     
==========================================
- Hits          108      106       -2     
+ Misses         21       20       -1     

Impacted Files	Coverage Δ
src/Mocking.jl	45.45% <ø> (ø)
src/mock.jl	81.25% <100.00%> (+2.46%)	⬆️
src/patch.jl	100.00% <100.00%> (ø)
src/expr.jl	100.00% <0.00%> (ø)
src/dispatch.jl	100.00% <0.00%> (ø)

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[omus]

Will add a test for #92