Remove undefined-function-is-assume-false from goto-instrument

[tautschnig]

Users can like-for-like replace such use with
--generate-function-body '.*' --generate-function-body-options assume-false.

Fixes: #2070

• 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.01%. Comparing base (b191cc1) to head (7382807).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8783   +/-   ##
========================================
  Coverage    80.01%   80.01%           
========================================
  Files         1700     1700           
  Lines       188345   188323   -22     
  Branches        73       73           
========================================
- Hits        150696   150692    -4     
+ Misses       37649    37631   -18     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

Pull request overview

Removes the --undefined-function-is-assume-false command-line option and its implementation from goto-instrument, directing users to replace it with --generate-function-body '.*' --generate-function-body-options assume-false.

Changes:

• Deleted undefined_function_abort_path API and implementation.
• Removed CLI option parsing and help/manpage documentation for --undefined-function-is-assume-false.
• Updated goto-instrument option list to no longer advertise the removed flag.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/goto-instrument/undefined_functions.h	Removes the declaration for the deleted undefined-function instrumentation helper.
src/goto-instrument/undefined_functions.cpp	Removes the implementation that rewrote undefined calls to assume(false).
src/goto-instrument/goto_instrument_parse_options.h	Drops the CLI option from the recognized options list.
src/goto-instrument/goto_instrument_parse_options.cpp	Removes runtime handling and --help text for the option.
doc/man/goto-instrument.1	Removes the manpage entry for the deleted option.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.