Removed obsolete and clean code.

[ymh199478]

Q	A
Branch?	v2.0(master)
Bug fix?	No
New feature?	No
Deprecations?	No
Internal Changed?	Yes
Removed	Yes
Tests pass?	Yes
Doc pr?	No

The commit removed the obsolete flag method，and clean the code.

[codecov-io]

Codecov Report

Merging #261 into master will increase coverage by 0.02%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
+ Coverage   90.21%   90.23%   +0.02%     
==========================================
  Files          35       35              
  Lines        2401     2397       -4     
==========================================
- Hits         2166     2163       -3     
+ Misses        235      234       -1

Impacted Files	Coverage Δ
src/CatLib.Core/Support/Str.cs	100% <ø> (+0.54%)	⬆️
src/CatLib.Core/Support/Extension/ExtendStream.cs	89.47% <100%> (-0.27%)	⬇️
src/CatLib.Core/CatLib/Facade.cs	94.87% <100%> (ø)	⬆️
src/CatLib.Core/Support/Arr.cs	97.48% <100%> (ø)	⬆️
src/CatLib.Core/Container/ExtendContainer.cs	69.39% <100%> (ø)	⬆️
src/CatLib.Core/Support/Helper.cs	100% <100%> (ø)	⬆️
src/CatLib.Core/Support/Extension/ExtendInt.cs	100% <100%> (ø)	⬆️
src/CatLib.Core/Support/SortSet.cs	90.76% <50%> (ø)	⬆️
src/CatLib.Core/Support/Stream/CombineStream.cs	92.1% <0%> (-0.11%)	⬇️
src/CatLib.Core/Support/Stream/SegmentStream.cs	97.14% <0%> (-0.08%)	⬇️

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