which system call gets called when rm command is given on the command line?
Or
Which are the system calls that get called when we want to delete a particular file through a command line?
Thank you.

Not sure what you mean by "system call". Commands that you enter in a terminal can be three types (minimum):
Built-in commands
Shell commands
Scripts (can call either built-ins or shell commands)

I believe you can tell a built-in by searching for it in the "executable" directories--eg: /bin /sbin /usr/bin etc. If there is no file to match the command, then it is built in to the kernel.
Note that this definition does not jibe with what I find in "Linux in a Nutshell", so I may be way off base.

For any purpose I can imagine, you will not care if it is shell or "built-in"

unlink.

You can see what gets called when you run command by running