Avoid explicit reference to 'mobile' in tethering_footer_info

The Hotspot & Tethering feature allows sharing the current primary
data connection of the device with others using either a Wi-Fi hotspot
or USB/Bluetooth/Ethernet tethering.

The primary data connection is typically a mobile data connection on a
phone, but that is not the case on other form factors, e.g. in the
desktop experience, where sharing your Ethernet connection via Wi-Fi
(i.e. Ethernet is the 'upstream' technology instead of
cellular/mobile) may be a much more common usecase.

Given that devices can support Hotspot & Tethering without supporting
Telephony, there should be no explicit reference to a "mobile data
connection", as it is not accurate.

Bug: 393312760
Test: Manual check
Flag: EXEMPT strings only change

Change-Id: If71134deca4610a2304630f331e3a4fe62f0bc63