Remove and replace use of look_through_casts

[tautschnig]

A function of this name was defined in two places, and all uses can
safely be replaced by skip_typecast.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a 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).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6544 (51c133c) into develop (6642254) will decrease coverage by 0.00%.
The diff coverage is 93.65%.

@@             Coverage Diff             @@
##           develop    #6544      +/-   ##
===========================================
- Coverage    75.99%   75.98%   -0.01%     
===========================================
  Files         1578     1578              
  Lines       180944   181029      +85     
===========================================
+ Hits        137500   137548      +48     
- Misses       43444    43481      +37     

Impacted Files	Coverage Δ
src/goto-instrument/contracts/assigns.h	100.00% <ø> (ø)
src/goto-instrument/contracts/contracts.h	100.00% <ø> (ø)
src/goto-instrument/contracts/utils.cpp	89.47% <78.57%> (-4.56%)	⬇️
src/goto-instrument/contracts/assigns.cpp	95.83% <90.00%> (-0.60%)	⬇️
src/goto-instrument/contracts/contracts.cpp	91.13% <98.46%> (-3.99%)	⬇️
jbmc/src/java_bytecode/java_pointer_casts.cpp	92.50% <100.00%> (-0.84%)	⬇️
...s/variable-sensitivity/interval_abstract_value.cpp	84.61% <100.00%> (-0.28%)	⬇️
src/goto-instrument/contracts/utils.h	100.00% <100.00%> (ø)
src/analyses/dirty.h	100.00% <0.00%> (ø)
... and 1 more

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