Bump DynamicPPL.jl, AdvancedVI, and Bijectors version

[torfjelde]

What the title says

Warning: this PR also removes testing of Tracker.jl. Tracker.jl is the only AD backend requiring custom rules (i.e. isn't supported by ChainRules.jl) and hence requires quite a bit of additional developer effort to maintain and test throughout the TuringLang ecosystem. It seems to me that this is no longer worth the effort given how little (if any) use Tracker.jl sees.

[coveralls]

Pull Request Test Coverage Report for Build 4735955139

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

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Totals
Change from base Build 4604993505:	0.0%
Covered Lines:	0
Relevant Lines:	1422

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💛 - Coveralls

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (3e71a76) 0.00% compared to head (1bb195c) 0.00%.

❗ Current head 1bb195c differs from pull request most recent head 966639f. Consider uploading reports for the commit 966639f to get more accurate results

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1979   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          21      21           
  Lines        1422    1424    +2     
======================================
- Misses       1422    1424    +2     

Impacted Files	Coverage Δ
src/essential/ad.jl	0.00% <0.00%> (ø)
src/inference/hmc.jl	0.00% <0.00%> (ø)
src/inference/mh.jl	0.00% <ø> (ø)
src/variational/VariationalInference.jl	0.00% <ø> (ø)
src/variational/advi.jl	0.00% <0.00%> (ø)

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[yebai]

Excellent PR -- thanks @torfjelde!

[devmotion]

@torfjelde I just noticed this change - this seems quite dangerous because things might start breaking silently without us noticing it while still stating officially in the package (compat entry, docs etc.) that Tracker is supported.

So I think in case this is the official policy (which IMO is a bit sad because Tracker is quite stable, much simpler than ReverseDiff or Zygote, and started to receive updates more frequently again) then IMO it should be removed from the package, docs, etc., ideally before removing tests for it.