Remove API v4 migration guide from nav
https://docs.gitlab.com/ee/api/v3_to_v4.html should not be included in the nav, so removes it from the nav.
Relates: gitlab!60714 (merged), which removes v3 to v4 migration guide.
Edited by Takuya Noguchi
https://docs.gitlab.com/ee/api/v3_to_v4.html should not be included in the nav, so removes it from the nav.
Relates: gitlab!60714 (merged), which removes v3 to v4 migration guide.