[Performance][PostRector] Remove alias exists check on NameImporter called from NameImportingPostRector

[samsonasik]

@TomasVotruba @staabm the alias exists check already in NameImportingPostRector before NameImporter->importName() called

rector-src/packages/PostRector/Rector/NameImportingPostRector.php

Lines 152 to 155 in 2faa19f

	$aliasName = $this->aliasNameResolver->resolveByName($name);
	if (is_string($aliasName)) {
	return new Name($aliasName);
	}

, so I think it no longer needed.

Ref rectorphp/rector#8077

[samsonasik]

All checks have passed 🎉 @TomasVotruba let's merge it to have faster feedback to test ;)