Revert signature help changes - conflicting requirements identified

TestSignatureHelpWithTriggers02 fails with both the original code and my attempted fixes. The test expects `bar`'s signature when the cursor is at `foo(bar()` after inserting `(`, but the logic for fixing nested call precedence conflicts with this expectation.

The fundamental issue is that the nested calls fix (showing outer call when cursor is after inner call's arguments) and the triggers test have opposite requirements for how to handle positions where multiple calls' applicable spans overlap.

Co-authored-by: jakebailey <[email protected]>

Author: Copilot