fixed issues discovered bj JET.jl

[dpinol]

Hi, after patching JET.jl with this not yet merged PR, it's now possible to run report_package(Metatheory) with Julia 1.8.

The current PR fixes most real issues reported by JET. Namely:

• It removes old functions which are never called, some of which are broken
• It fixes references to undefined variables
• It adds something(x) after checking x !== nothing to get more optimized code.

[codecov-commenter]

Codecov Report

Merging #138 (c2afdce) into master (305a9d2) will increase coverage by 0.20%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #138      +/-   ##
==========================================
+ Coverage   76.64%   76.84%   +0.20%     
==========================================
  Files          15       15              
  Lines        1400     1382      -18     
==========================================
- Hits         1073     1062      -11     
+ Misses        327      320       -7     

Impacted Files	Coverage Δ
src/EGraphs/analysis.jl	85.18% <0.00%> (+1.03%)	:arrow_up:
src/EGraphs/saturation.jl	93.33% <0.00%> (-0.08%)	:arrow_down:
src/Rewriters.jl	32.32% <0.00%> (ø)
src/utils.jl	37.93% <ø> (+1.08%)	:arrow_up:
src/EGraphs/egraph.jl	89.68% <100.00%> (-0.17%)	:arrow_down:
src/EGraphs/ematch.jl	92.00% <100.00%> (-0.07%)	:arrow_down:
src/EGraphs/Schedulers.jl	39.18% <0.00%> (-0.82%)	:arrow_down:
src/Patterns.jl	72.34% <0.00%> (-0.58%)	:arrow_down:
... and 3 more

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[0x0f0f0f]

I guess the failures are not related to this MR, but I still have to check manually, I'll merge after checking. Thanks a lot

[dpinol]

fyi, latest 0.6.2 release can now analyse Metatheory.jl