Fix deleteRange behavior

[skhugh]

What this PR does / why we need it?

Changed deleteRange to cut off target node from the tree, as it can be later requested to be deleted on GC.
Also changed the naming to cutOffRange to better suit the changed behavior.

Any background context you want to provide?

What are the relevant tickets?

Fixes #

Checklist

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

[codecov]

Codecov Report

Merging #81 (1ff6867) into main (f2cf37d) will decrease coverage by 0.03%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
- Coverage   81.40%   81.38%   -0.03%     
==========================================
  Files          52       52              
  Lines        2377     2374       -3     
  Branches      336      336              
==========================================
- Hits         1935     1932       -3     
  Misses        257      257              
  Partials      185      185              

Impacted Files	Coverage Δ
...in/kotlin/dev/yorkie/document/crdt/RgaTreeSplit.kt	66.66% <0.00%> (ø)
...ie/src/main/kotlin/dev/yorkie/util/SplayTreeSet.kt	77.94% <100.00%> (-0.32%)	⬇️

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