drop files_external tests from autotest - they will be executed with aut...

...otest-external.sh which is coming

see #12168 for the autotest-external.sh

This just drops all those skipped tests.

Without this (sqlite only):
```
Time: 3.06 minutes, Memory: 129.75Mb
624 skipped tests
```

With this (sqlite only):
```
Time: 2.38 minutes, Memory: 98.25Mb 
107 skipped tests 
```

cc @LukasReschke @DeepDiver1975