Revert "Fixed XPath AST for :last-of-type"

Axes can't be used in combination with functions.

This reverts commit b0b572a5846a884bcd267f8b0dc638dd511e9f52.
Reverted AST changes for first-of-type

Functions can't be used in combination with axes, so I'll just need to fix the
position() function to work properly.