Definition: In this task, you need to remove all words of a given length in the sentence. The number of letters in a word determine its length, for example, the length of the word "apple" is 5.
Input: Sentence: 'a dog is sitting in a field of grass waiting for someone to occupy an empty chair'. Remove all words of length '7' in the given sentence.

a dog is in a field of grass for to occupy an empty chair