Revert pipeline processor invalid field access check due to regression

[patrickmann]

Resolves #18017

#16029 was designed to flag illegal expressions like <array>.[<index>] in a pipeline rule. However, we end up also blocking legal expressions, e.g. to access JSON fields of type array. JSON parsing allows using dot notation or square brackets interchangeably.

This PR reverts the change.

How Has This Been Tested?

Parser behaves as before:

• Able to access GeoIP subdivisions data in a pipeline rule
• rs.["a"] does not trigger a syntax error; error message visible in server log