simplify the remove_exceptions API

[kroening]

This removes the usage of a pointer an the potential to call the variant
that does remove_instanceof without class hierarchy.

• 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.
• 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.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[smowton]

Name not really accurate; this should only affect the newly introduced instanceof instructions, not existing ones

[kroening]

Ok, will flip naming around.

[smowton]

Any new instanceof instructions

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: 0cdc1f0).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/90551420
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.

[peterschrammel]

@thk123, @allredj, this is going to break TG, but trivial to fix.

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: 902cc69).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/90679994
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.

[tautschnig]

Please rebase to re-trigger the bot.

[thk123]

I wouldn't bother - this needs a manual bump, I believe @allredj is looking at this.

[tautschnig]

Marked do-not-merge and assigned to @allredj.

[allredj]

Test-gen PR is here: https://github.com/diffblue/test-gen/pull/2457. Will notify when passing.

[allredj]

TG bump passing. Good to merge.