mu4e 1.4 brings quite a few changes, including the deprecation of
previously used variables. These are now guarded by a version
comparison. org-mu4e is not needed for linking anymore,
org-mu4e-link-query-in-headers-mode was renamed. It's new version
defaults to nil and is therefore not set anymore -- I am not sure if the
default was changed or setting it was not strictly needed previously.
- if module workspaces is not used, an error would be raised when calling =mu4e
`=mu4e: Symbol’s function definition is void: +workspace-switch`
- if module workspaces is not used, an error would be raised when quiting mu4e
`=mu4e: Symbol’s function definition is void: +workspace/delete`
