Remove Pointer_byte_extract8 as it is no longer needed.

[NlightNFotis]

It was noted in #2995
that this test is no longer needed as the case it tests for
is covered by Pointer_byte_extract5/no-simplify.desc

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
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[codecov]

Codecov Report

Merging #5917 (e5e4a18) into develop (46449ee) will increase coverage by 0.18%.
The diff coverage is 96.13%.

@@             Coverage Diff             @@
##           develop    #5917      +/-   ##
===========================================
+ Coverage    73.37%   73.55%   +0.18%     
===========================================
  Files         1428     1430       +2     
  Lines       155121   155222     +101     
===========================================
+ Hits        113813   114170     +357     
+ Misses       41308    41052     -256     

Impacted Files	Coverage Δ
jbmc/src/java_bytecode/assignments_from_json.cpp	97.26% <ø> (ø)
jbmc/src/java_bytecode/java_class_loader.cpp	96.07% <ø> (ø)
jbmc/src/java_bytecode/java_object_factory.cpp	94.29% <ø> (ø)
src/analyses/reaching_definitions.cpp	77.58% <ø> (ø)
src/analyses/reaching_definitions.h	82.75% <ø> (ø)
...ses/variable-sensitivity/abstract_value_object.cpp	95.43% <ø> (ø)
...s/variable-sensitivity/interval_abstract_value.cpp	81.96% <ø> (ø)
...sitivity/variable_sensitivity_dependence_graph.cpp	84.58% <ø> (ø)
...variable-sensitivity/variable_sensitivity_domain.h	100.00% <ø> (ø)
...ensitivity/variable_sensitivity_object_factory.cpp	97.61% <ø> (ø)
... and 145 more

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