refactor(adb): remove outdated completion plugin `adb` (#12576)

BREAKING CHANGE: the `adb` plugin has been removed in favor of the completion
provided out-of-the-box by zsh since 4.3.14.

This commit removes plugin `adb`, which bundles custom completion for the
`adb` tool for Android. `adb` completion is already supported out of the
box in zsh 4.3.14 and older.

Reference: https://github.com/zsh-users/zsh/commit/d1a557d008b7fa7881327acbd6decdb50631cc9c