Remove unused validation of cast to imported anon type

[MaryamZi]

Purpose

$title. No longer required with the changes in #29792.

[codecov]

Codecov Report

Merging #30410 (1505853) into master (344527d) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #30410      +/-   ##
============================================
+ Coverage     68.23%   68.25%   +0.02%     
+ Complexity    37298    37297       -1     
============================================
  Files          2895     2895              
  Lines        158485   158432      -53     
  Branches      19718    19707      -11     
============================================
- Hits         108144   108141       -3     
+ Misses        44003    43951      -52     
- Partials       6338     6340       +2     

Impacted Files	Coverage Δ	Complexity Δ
...g/wso2/ballerinalang/compiler/desugar/Desugar.java	86.20% <ø> (+0.89%)	918.00 <0.00> (ø)
.../java/io/ballerina/projects/PackageResolution.java	86.86% <0.00%> (-2.03%)	31.00% <0.00%> (ø%)
...ang/compiler/semantics/model/types/BUnionType.java	79.14% <0.00%> (-1.43%)	85.00% <0.00%> (-2.00%)
...runtime/internal/scheduling/WorkerDataChannel.java	88.53% <0.00%> (+0.63%)	34.00% <0.00%> (ø%)
.../ballerina/runtime/internal/scheduling/Strand.java	81.11% <0.00%> (+1.66%)	45.00% <0.00%> (+1.00%)

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