Minor class transform cleanups

[JLHwung]

Q	A
Tests Added + Pass?	Yes
License	MIT

Two minor cleanups about class / class properties transform:

• The first one get rid of a @ts-expect-error comment.
• The second one generally improves the thisContextVisitor performance as now we don't have to access the parent node for every ThisExpression node.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/54658/