Crangler: also apply remove-static to declarations

[tautschnig]

Taking functions out of file-local scope requires removing the "static"
keyword from both definitions as well as declarations.

• 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 #6816 (c5f0f36) into develop (5ff1a04) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #6816   +/-   ##
========================================
  Coverage    77.00%   77.00%           
========================================
  Files         1594     1594           
  Lines       184348   184350    +2     
========================================
+ Hits        141954   141957    +3     
+ Misses       42394    42393    -1     

Impacted Files	Coverage Δ
src/goto-instrument/contracts/memory_predicates.h	100.00% <ø> (ø)
src/crangler/c_wrangler.cpp	59.33% <100.00%> (+0.75%)	⬆️
src/goto-instrument/contracts/contracts.cpp	93.89% <100.00%> (ø)
...rc/goto-instrument/contracts/memory_predicates.cpp	85.49% <100.00%> (ø)

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