Revert the referenced structures part of batfish/batfish#6249

[dhalperi]

It's expensive in rare cases, and also significantly more expensive to turn into
IntegerSpace dynamically (deep in a nested map).

[batfish-bot]

This change is 

[progwriter]

Reviewed 18 of 18 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @anothermattbrown)

[codecov]

Codecov Report

Merging #6261 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #6261      +/-   ##
============================================
- Coverage     72.89%   72.89%   -0.01%     
+ Complexity    35003    35000       -3     
============================================
  Files          2832     2832              
  Lines        142263   142258       -5     
  Branches      17085    17082       -3     
============================================
- Hits         103705   103701       -4     
- Misses        30324    30328       +4     
+ Partials       8234     8229       -5     

Impacted Files	Coverage Δ	Complexity Δ
...rencedstructures/ReferencedStructuresAnswerer.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...del/answers/ConvertConfigurationAnswerElement.java	95.34% <100.00%> (ø)	21.00 <1.00> (ø)
...n/java/org/batfish/vendor/VendorConfiguration.java	97.24% <100.00%> (ø)	50.00 <2.00> (-1.00)
...sh/question/UndefinedReferencesQuestionPlugin.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)
...src/main/java/org/batfish/coordinator/WorkMgr.java	75.69% <0.00%> (-0.32%)	245.00% <0.00%> (-1.00%)
...tfish/representation/cisco/CiscoConfiguration.java	85.91% <0.00%> (-0.14%)	492.00% <0.00%> (-1.00%)
.../org/batfish/dataplane/ibdp/BgpRoutingProcess.java	82.11% <0.00%> (+0.41%)	131.00% <0.00%> (-1.00%)	⬆️
...src/main/java/org/batfish/coordinator/PoolMgr.java	60.49% <0.00%> (+1.23%)	16.00% <0.00%> (+1.00%)
...main/java/org/batfish/datamodel/acl/AclTracer.java	61.63% <0.00%> (+1.25%)	44.00% <0.00%> (+1.00%)