A Google word frequency graph (N-gram graph) shows that "no point in doing" is most common in American books. https://books.google.com/ngrams/graph?content=no+point+in+doing%2Cno+point+to+doing%2Cno+point+doing&year_start=1800&year_end=2019&corpus=en-US-2019&smoothing=3

If you omit "in", you will have a grammatically correct sentence but it will not mean what you want it to mean. A preposition is needed, and the best one would be "to", not "in". If you omit "in", "doing" becomes an adjective that modifies "point", so the meaning is nonsensical. To understand this better, consider the good sentence "There is no couple dancing the cha-cha." That makes sense because "dancing" does describe the couple. When you say "there is no point doing it that way" you are saying that there are no points that are doing it that way. It is absurd. Points never do things. However, people do make this mistake frequently.

the word "in" can't be omitted in such sentence

it

Although I agree with Jack that on a test such as IELTS "in" cannot be omitted in your sentence, in real life it is dropped all the time, at least in American English. Your goals shape the kind of English you learn. If you're preparing for a test or you're in university using English, forget what I said and stick to Jack's answer. But if you're moving to America or Canada or you watch a lot of movies/TV, be prepared for the some of the "rules" to be "broken" by native speakers (Not all, and not all the time). Not trying to spark any debate here, just reflecting on the fact that English in the textbooks / on most tests is not what you always get in real life.