ansi-c: remove duplicate loc() invocations from scanner

[kroening]

This removes repeated calls to loc() from the ANSI-C scanner.

• 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/
• n/a 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

Attention: Patch coverage is 0% with 32 lines in your changes missing coverage. Please review.

Project coverage is 80.36%. Comparing base (cbdab7f) to head (7b1ae4a).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/ansi-c/scanner.l	0.00%	32 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8626      +/-   ##
===========================================
- Coverage    80.36%   80.36%   -0.01%     
===========================================
  Files         1686     1686              
  Lines       206799   206800       +1     
  Branches        84       84              
===========================================
  Hits        166200   166200              
- Misses       40599    40600       +1     

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