I was just always confused about this concept. Is it impossible to just erase an amendment? Does it say anything in the Constitution about repealing an Amendment.
It is actually the 21st Amendment that repealed Prohibition.
Section 1 of the 21st amendment reads: The eighteenth article of amendment to the Constitution of the United States is hereby repealed.
So basically, the 21st amendment did remove the 18th amendment.
There are two ways that amending constitutions is done. One way, which is how laws are amended in the US (the Australian Constitution is amended this way) is to remove text, add text, or both. Another way, which is how the US Constitution is done (I don't know if any other countries do it this way) is to add the amendments after the Constitution. Consequently, any text within the Constitution, or previous amendments, stays there, it's just rendered ineffective by later amendment.
With regards to the 21st Amendment, it didn't simply repeal the 18th Amendment. The second part says
Section 2. The transportation or importation into any State, Territory, or possession of the United States for delivery or use therein of intoxicating liquors, in violation of the laws thereof, is hereby prohibited.
This section actually has consequences. From Wikipedia, "Section 2 has been the source of every Supreme Court ruling directly addressing Twenty-first Amendment issues."
The precise details are quite technical, but check out that section of the Wikipedia page if interested. Basically, the 21st Amendment give States quite a bit of control over alcohol within their state, more than they would have otherwise.
The 21st Amendment did remove the 18th, legally speaking.
That being said, most published versions of the Constitution include the 18th Amendment because it's historically relevant (and the 21st Amendment wouldn't make sense if you read the text unless you know what the 18th Amendment was, since it mentions the 18th).