So, one usually has a choice: on the one hand an article should describe new and interesting results, without technical stuff interesting for 5% of readers or less. On the other hand, It might be a good idea to keep all the relevant material in the same place. This may be useful for further work of authors, or also for somebody else, who wants to learn from the paper or to work out something similar.
Recently there was a post by "How many deleted sections do you write?", where Daniel Lemire proposes a good idea what to do with deleted pages. Daniel suggests to put them in the article's supplementary material, with a reference in the article. In such a way, one can expect the article to be easily read with an access to all necessary details.
Another way might be to keep all the omitted material in the arXiv preprint, and cite it in the forthcoming paper.