Search query fixup: remove Input reference in ParseTree [2/3]

Created by: rvantonder

This stacked diff depends on #6114.

This is a semantics preserving change.

Summary

Basically went through this question:

This reference to Input in query.go seems unnecessary, what happens if I remove it?

And everything turns out better. What this does:

• Removes the Input reference
• Renames the query.go file to parse_tree.go.

Test plan: This is a refactor, tests are updated.