Remove old SHM files left from the previous runs because of crashes

[ldorau]

Description

Remove old SHM files /tmp/umf_file_provider_*
(at the beginning of the test)
left from the previous runs, because of crashes
of the ipc_file_prov test.

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly

[ldorau]

We cannot use tmpfile() nor mkstemp(), because those functions create and open a temporary file on their own, but we pass only a name of the file to the file provider and it opens this file on its own - we cannot force file memory provider to use only temporary files.

[lukaszstolarczuk]

We cannot use tmpfile() nor mkstemp(), because those functions create and open a temporary file on their own, but we pass only a name of the file to the file provider and it opens this file on its own - we cannot force file memory provider to use only temporary files.

mktemp is would you're looking for, but the current solution is as good, I believe.
/tmp files are deleted on reboot... but we almost never do it 😉