I thought one of the amendments to the constitution made it so that state legislatures could no longer remove a sitting senator.
I would to God we still have that ability!
While many of the older states had procedures for the impeachment of a US Senator by a state legislature, those provisions were never executed because there was no provision in the US Constitution to allow it. Article VI of the US Constitution, aka the Supremacy Clause, makes it superior to all state constitutions.
The 17th Amendment only changed the method of election of US Senators and said nothing about possible removal.
Federal officers may only be removed by loss of an election, resignation, death or expulsion by his particular House of Congress. This issue has been litigated in both federal and state court, and is settled law.