settings_account: Fix error message while deactivating account.
settings_account: Fix error message while deactivating account.

We were showing the incorrect error message when the user who
is trying to deactivate himself is the last owner. This commit
fixes this to show "Cannot deactivate the last organization owner"
instead of "Cannot deactivate the last organization administrator".

We had already removed the restriction for deactivating last admin
and added it for last owner, while adding the new owner role.

hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,rht/zulip,punchagan/zulip,kou/zulip,zulip/zulip,rht/zulip,zulip/zulip,kou/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,showell/zulip,hackerkid/zulip,kou/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,showell/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,showell/zulip,hackerkid/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,rht/zulip,punchagan/zulip,showell/zulip,andersk/zulip,zulip/zulip,showell/zulip,rht/zulip,punchagan/zulip