Remove preprocessing that was using ID_cprover_string_concat_bool_func

[romainbrenguier]

This builtin function is not handled by the solver, so preprocessing functions
and producing ID_cprover_string_concat_bool_func could only lead to
errors.
Instead we use models of these functions given in the java-models-library (updated with this PR to include these models).

3719036

• Each commit message has a non-empty body, explaining why the change was made.
• [na] 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).
• [na] My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• [na] White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 3719036).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/92000703

[romainbrenguier]

this was merged a bit too quickly because the corresponding submodule is not merged on master yet diffblue/java-models-library#14 ; I should have added a "do not merge" label...

[allredj]

DO NOT DELETE THE REMAINING BRANCH!

[tautschnig]

Apologies for the overly eager merge. But also there is a problem with the workflow here. If all tests pass, including the TG bot, but still a merge is not indicated, then there isn't sufficient testing in place.

[romainbrenguier]

Here a new PR to update to the merge on master #3449

[tautschnig]

So the rules should be:

1. Don't create a PR if the submodule has not been merged yet or
2. If you want a PR, e.g., for testing purposes, mark it as "do not merge" until the submodule pointer is to a commit in master?

[romainbrenguier]

@tautschnig we do want PRs for the submodule to make sure we are not breaking CI on cbmc, so we should go for option 2

[romainbrenguier]

anyway, as long as the java-models-library branch is not deleted, nothing bad should happen