There is another possibility, if we remove the robots and the laws from the question, but keep a time traveller killing Asimov. The story is "One Rejection Too Many" (1978) by Patricia Nurse (her only professional SF story).
Anthologized in Space Mail, it was originally published in Asimov's, July-August 1978 and can be read at the Internet Archive. The story takes the form of an exchange of letters between one Nancy Morrison and Isaac Asimov in his presumptive capacity of editor of Asimov's. (The epistolary format is what qualified it for inclusion in Space Mail.)
The letters consist of series of submission letters from one Nancy Morrison, who claims to have a time-traveller, Vahl, from c.5000 CE as a houseguest. Vahl has written an account of the world in his time, and wishes to have it published. The responses are a series of rejection letters, accompanied by various suggestions for improvement of the story, with Asimov treating the story of the time-traveller as an amusing hook.
The first version is rejected for lacking plot and characterization; the second for being a soap opera with an excess of sexual content. An attempt to add humour is panned as not being sophisticated enough:
P.S. Have you considered reading your story, as it is, on The Gong Show?
The final submission letter informs Asimov that the time-traveller was livid and has made one final rewrite before departing, but has "made some long overdue improvements to our time frame as a parting gift."
The final response comes from George H. Scithers, Editor, Arthur C. Clarke's Science Fiction Magazine who is confused by the reference to Isaac Asimov, but happy to accept the story.
Dear Miss Morrison,
I am very confused by your letter. Who is Isaac Asimov? I have checked with several publishers and none of them has heard of Isaac Asimov's Science Fiction Magazine, although the address on the envelope was correct for this magazine.
However, I was very impressed with your story and will be pleased to accept it for our next issue. Seldom do we receive a story combining such virtues as a well-conceived plot, plenty of human interest, and a delightfully subtle brand of humor.