Remove support for nested virtual properties

[Cisphyx]

A large part of this is naming cleanup (adjusting virts -> virt)

[codecov]

Codecov Report

❌ Patch coverage is 97.14286% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.46%. Comparing base (3a8ef8c) to head (8e686ac).
⚠️ Report is 1 commits behind head on synapse-3xx.

Files with missing lines	Patch %	Lines
synapse/lib/ast.py	94.35%	11 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           synapse-3xx    #4885      +/-   ##
===============================================
+ Coverage        96.34%   96.46%   +0.11%     
===============================================
  Files              259      259              
  Lines            63173    63060     -113     
===============================================
- Hits             60864    60830      -34     
+ Misses            2309     2230      -79     

Flag	Coverage Δ
linux	96.46% <97.14%> (+0.11%)	⬆️

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