Removes the three remaining instances of `settings_html` links in
the integrations documentation. Use of `settings_html` was removed
from the general shared `create-an-incoming-webhook.md` and
`create-a-generic-bot.md` files in e9e2721.
The "subdomain" label is redundant, to the extent it's even
accurate -- this is really just the URL we want to display,
which may or may not involve a subdomain. Similarly "external".
The former `external_api_path_subdomain` was never a path -- it's a
host, followed by a path, which together form a scheme-relative URL.
I'm not quite convinced that value is actually the right thing in
2 of the 3 places we use it, but fixing that can start by giving an
accurate name to the thing we have.
Mateusz Mandera
Lauryn Menard
Anders Kaseorg
gr455
Anders Kaseorg
novokrest
Greg Price
Eeshan Garg
Aditya Bansal