The term 注销 appeared before the existence of computers, which is the antonym of 注册 (register). As a result, 注销 means "unregister", i.e. cancel the account. This term is usually used in banks, such as 注销银行账号 (unregister the bank account).
However, after computers became popular, Microsoft uses 注销 as the official translation of "log off" in its Windows operating system. This usage is absolutely wrong, but this usage is well-known because of the popularity of Microsoft Windows, and becomes gradually accepted by native Chinese speakers, and therefore many people use this "wrong" term.
The term 退出 also appeared before the existence of computers, which means "exit" or "quit".
The term 登出 appeared after the popularity of computers, which is an modern made-up term intentionally for the Chinese translation of "log out", because etymologically, 登出 is the antonym of 登入 (log in), although the "more correct" Chinese term for "log in" should be 登录.
In a word, the correct term of "log out" should be 退出 or 登出, which is often used in Google and Baidu. 退出 is used more often.