Implement Protocol Changes for Tree.RemoveStyle

[raararaara]

What this PR does / why we need it?

This PR reflects protocol changes for the Tree.RemoveStyle patch on #745.

Any background context you want to provide?

• Proto file and converter were modified to reflect requirements related to the Tree.RemoveStyle patch.
• Added related test code.

What are the relevant tickets?

Related #745, yorkie-team/yorkie#748

Checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.77%. Comparing base (0bc7ce1) to head (64f74fb).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #755      +/-   ##
==========================================
+ Coverage   81.50%   81.77%   +0.26%     
==========================================
  Files          59       59              
  Lines        4348     4357       +9     
  Branches      853      856       +3     
==========================================
+ Hits         3544     3563      +19     
+ Misses        543      537       -6     
+ Partials      261      257       -4     

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[hackerwins]

@raararaara Is there no need to add related test codes?

Please also add a brief explanation.

What this PR does / why we need it?
Any background context you want to provide?
What are the relevant tickets?
Related #745, yorkie-team/yorkie#748

[raararaara]

@raararaara Is there no need to add related test codes?

Please also add a brief explanation.

What this PR does / why we need it?
Any background context you want to provide?
What are the relevant tickets?
Related #745, yorkie-team/yorkie#748

I have added the relavent test code and added a brief explanation.

[hackerwins]

LGTM.