Would it be possible to get rid of an amendment in the United States?

THAT WOULD REQUIRE A CONSTITUTIONAL AMENDMENT

Congress nullifies an Amendment by passing a new Amendment, a la the 21st that de facto repealed the 18th (and ended Prohibition). 

No.  However; you can pass a new admendment that nillifies it.

No, there is no provision to "get rid" of a Constitutional Amendment.  An Amendment can repeal a previous Amendment.  The obvious example is the 18th Amendment (Prohibition) which was repealed by the 21st Amendment.  The 18th Amendment still exists; a repeal is not a "get rid of".

Of course.  Although technically that is done by passing a new amendment that repeals the earlier amendment.

This has in fact been done before.  The 21st Amendment was passed to repeal the 18th Amendment.

https://en.wikipedia.org/wiki/Twenty-first_Amendme...