Fix process of tree style change

[humdrum]

What this PR does / why we need it:

• RHT that storing attributes is shallowly copied, So the style set does not perform at yorkie tree.
• Remove unnecessary code.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 38.89%. Comparing base (e309688) to head (b8eeff9).

Files	Patch %	Lines
Sources/Document/CRDT/CRDTTree.swift	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #170   +/-   ##
=======================================
  Coverage   38.89%   38.89%           
=======================================
  Files         105      105           
  Lines       18895    18893    -2     
=======================================
  Hits         7349     7349           
+ Misses      11546    11544    -2     

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[myupage]

thank you