[CI] Remove SBA PLC job dependencies, remove create_ref and create_ref_part2 marks, correct coverage job

• Related issues: #1167 (closed)
• Requested reviewers: @jiaquan.huo, @kiene, @tamarapu, @pihlajakuja

Reason why this change is needed

The SBA PLC jobs depends on previous jobs to finish. The MR sa4/audio/ivas-basop!428 (closed) seems to fail due to an error as result of this dependency. The failures are difficult to reproduce and seem to depend on the timing of the jobs during execution.

The SBA PLC job dependency is the background for using the marks create_ref and create_ref_part2. These have been used during reference creation to resolve the dependency by two sequential pytest calls. Since the DuT tests run without these marks, DuT encoder functions have been moved to the create_ref stage, which may be confusing. Removing the dependency between the SBA PLC jobs would simplify maintenance of the tests. These marks should resolve the mentioned dependency, but it does not seem to be working as intended.

Description of the change

• Added encoding of bitstreams for each PLC case, removing test_sba_plc_system dependency on test_sba_enc_system.
• Removed marks create_ref and create_ref_part2.
• Removed "dutenc" DuT encoding files during reference creation.
• Moved --use_ltv cases in coverage job. The coverage job produces two reports, one for stv and one for ltv and EVS. The SBA LTV tests were in the stv section.

Affected operating points

• All tests and results should be the same.
• Increased runtime for SBA PLC tests, since the combination of a bitstream and PLC pattern now triggers the same encoder bitstream to be generated several (3) times. Once for each of the plc_patterns = ["PLperc12mblen5", "PLperc40mblen50", "PLperc42mblen2"].
  • ** Edit: Runtime decreased instead of increased!**

Related to #1167 (closed)