You mean "Why doesn't Perl have a function named 'remove'?" Because it doesn't. This is exactly the same reason why Perl doesn't have a function named "insert." It may be obvious to you what a remove function would do, but it does beg the question "remove what?"

A lot of functions that interact with the file system are derived from Unix system calls, and unlink is one of them.

Incidentally, your node title is not terribly informative. It could easily mean "what is the remove function," "how does one remove a function," or "where is the function named remove?" Indeed, my first interpretation was the second, whereas your meaning seems to be closer to the third.