[mkannwischer]

ubuntu-latest (which is used to build the CBMC docs) has started migration from Ubuntu 24.04 to 26.04 which results in Doxygen to upgrade from 1.9.8 to 1.15.0.
This upgrade resulted in pages disappearing from the rendered docs including
https://diffblue.github.io/cbmc/memory-bounds-checking.html. Doxygen 1.15 applies an \ingroup that precedes \page to the page, which renders the page inline into group__module__hidden.html instead of as a standalone page.

This commit removes \ingroup module_hidden from the affected pages which renders correctly in 1.9.8 and 1.15.0 as far as I can tell.

• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.