dictionary-form + よう
means "so as to ~", "so that ~", etc. See this article.- 必要のない部分 literally means "the part where there is not necessity". 必要のない is a relative clause that adjectivally modifies 部分, and の can be used in place of が in relative clauses. See: How does the の work in 「日本人の知らない日本語」?How does the の work in 「日本人の知らない日本語」? Of course you can simply translate it as "unnecessary parts".
- した is not an imperative form. This sentence is not an order but a neutral sentence with the omitted subject (="I"). The last half literally means "I omitted unnecessarily parts", but you can translate it also as "unnecessary parts were omitted".