remove attribute where it does not apply

```
gflags.h(226): warning: attribute "visibility" does not apply here
```

The visibility attribute applies to symbols like functions and variables. A definition of an enumeration type that doesn't contain a variable name doesn't create any symbols.
.gitlab-ci.yml not found in this commit
Status Job ID Name Coverage
  Build
failed #2329
build

 
  Test
skipped #2331
allowed to fail
code_quality
skipped #2335
allowed to fail
container_scanning
skipped #2334
allowed to fail
dependency_scanning
skipped #2332
allowed to fail
license_management
skipped #2333
allowed to fail
sast
skipped #2330
test
 
Name Stage Failure
failed
build Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job trace