Remove the __CPROVER_HIDE label when inlining

[tautschnig]

Leaving this label in place will mark the function being inlined into as hidden,
which messes up, e.g., coverage instrumentation.

Consider hidden.c:

#include <string.h>
int foo() { char *a, *b; return memcmp(a, b, 1); }
int main() { foo(); return 0; }

goto-cc hidden.c
goto-instrument --add-library a.out b.out (add library function with hiding)
goto-analyzer --simplify c.out b.out (goto-analyzer does inlining)
cbmc --cover location c.out (will be missing any coverage targets in foo)
cbmc --cover location b.out (has coverage targets in foo)

With this patch, cbmc --cover location c.out also has coverage targets in foo.

• Each commit message has a non-empty body, explaining why the change was made.
• My contribution is formatted in line with CODING_STANDARD.md.
• n/a 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.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[allredj]

This PR failed Diffblue compatibility checks (cbmc commit: f2306e3).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/87246538
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).

[allredj]

Passed Diffblue compatibility checks (cbmc commit: f2306e3).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/87246538