Stop trying to parse deleted schema files

[QMalcolm]

resolves #8860

Problem

Waaaay back (in 7563b99) deleted schema files started being separated out from deleted non-schema files. However, ever since when it came to scheduling files for re-parsing, we've only done so for deleted non-schema files. We even missed this when we refactored the scheduling code in b37e5b5. This means when schema files got deleted and then the project went through partial parsing, you were likely to see an error like the following

05:53:11 Traceback (most recent call last):
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 87, in wrapper
    result, success = func(*args, **kwargs)
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 72, in wrapper
    return func(*args, **kwargs)
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 143, in wrapper
    return func(*args, **kwargs)
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 172, in wrapper
    return func(*args, **kwargs)
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 219, in wrapper
    return func(*args, **kwargs)
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/cli/requires.py", line 246, in wrapper
    manifest = ManifestLoader.get_full_manifest(
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/parser/manifest.py", line 316, in get_full_manifest
    manifest = loader.load()
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/parser/manifest.py", line 492, in load
    self.parse_project(
  File "/venv/dbt-1.6.0-latest/lib/python3.8/site-packages/dbt/parser/manifest.py", line 659, in parse_project
    block = FileBlock(self.manifest.files[file_id])
KeyError: 'salesforce_opportunity://models/marts/core/metrics.yml'

We've over the years added more things you could define in schema files, which in turn means schema files have been changing (and getting deleted) more frequently. Thus we've been seeing this error crop up more and more.

Solution

Not scheduling deleted schema files for parsing (like we've always been doing for deleted non-schema files)

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.02%. Comparing base (fc43101) to head (9f22326).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9722      +/-   ##
==========================================
- Coverage   88.08%   88.02%   -0.07%     
==========================================
  Files         178      178              
  Lines       22419    22439      +20     
==========================================
+ Hits        19747    19751       +4     
- Misses       2672     2688      +16     

Flag	Coverage Δ
integration	85.48% <100.00%> (-0.14%)	⬇️
unit	62.24% <0.00%> (-0.02%)	⬇️

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