[T-Mobile Samsung Galaxy S8 Questions & Answers] Edje:
For Android 8.0+ :

1. First, download AutoNotification

2. Then, open the app and under "Standalone Features" tap "Notification Blocking"

3. Now tap the plus in the upper right and search for "calling"

4. An app called "Wi-Fi Calling" will show up. Tap it. Next a box that says "All Fields Optional" will show up. Just tap OK.

There! You're done! The notification won't show up again unless you remove it from that list and restart your phone!

This method works for any app including the Wi-Fi Calling app. It does not keep the app from running, which means Wi-Fi calling will still work fine while the notification is blocked.

For Android Under 8.0 :

All that needs to be done is force stopping the wifi calling package when you connect to wifi. The package restarts automatically (but does not send the notification again) and I've tested that wifi calling and texting will work fine while using this profile. If wifi disconnects and reconnects the notification will show up again, so the profile stops the package everytime you connect to a network.

The profile will wait 6 seconds after connection to wifi to stop the package (and get rid of the notification) as this is how long it takes for the notification to show up on my phone after I connect to wifi. If the profile doesn't work try tweaking this time to a longer amount of seconds.

Here's the XML for the profile:

<TaskerData sr="" dvi="1" tv="5.1m">
<Profile sr="prof11" ve="2">
<cdate>1518069433891</cdate>
<edate>1518070561772</edate>
<id>11</id>
<mid0>10</mid0>
<nme>Stop wifi calling notif</nme>
<State sr="con0" ve="2">
<code>160</code>
<Str sr="arg0" ve="3"/>
<Str sr="arg1" ve="3"/>
<Str sr="arg2" ve="3"/>
<Int sr="arg3" val="0"/>
</State>
</Profile>
<Task sr="task10">
<cdate>1518069188395</cdate>
<edate>1518070421848</edate>
<id>10</id>
<nme>Stop wifi</nme>
<Action sr="act0" ve="7">
<code>30</code>
<Int sr="arg0" val="0"/>
<Int sr="arg1" val="6"/>
<Int sr="arg2" val="0"/>
<Int sr="arg3" val="0"/>
<Int sr="arg4" val="0"/>
</Action>
<Action sr="act1" ve="7">
<code>465073209</code>
<Bundle sr="arg0">
<Vals sr="val">
<com.mobizsystems.mdm.tasker.key>3</com.mobizsystems.mdm.tasker.key>
<com.mobizsystems.mdm.tasker.key-type>java.lang.Integer</com.mobizsystems.mdm.tasker.key-type>
<com.mobizsystems.mdm.tasker.packages><StringArrayList sr=""><_arrlst_com.mobizsystems.mdm.tasker.packages0>com.samsung.tmowfc.wfcpref</_arrlst_com.mobizsystems.mdm.tasker.packages0><_arrlst_com.mobizsystems.mdm.tasker.packages1>com.samsung.tmowfc.wfccontroller</_arrlst_com.mobizsystems.mdm.tasker.packages1></StringArrayList></com.mobizsystems.mdm.tasker.packages>
<com.mobizsystems.mdm.tasker.packages-type>java.util.ArrayList</com.mobizsystems.mdm.tasker.packages-type>
<com.twofortyfouram.locale.intent.extra.BLURB>Force Stop 2 packages</com.twofortyfouram.locale.intent.extra.BLURB>
<com.twofortyfouram.locale.intent.extra.BLURB-type>java.lang.String</com.twofortyfouram.locale.intent.extra.BLURB-type>
<net.dinglisch.android.tasker.subbundled>true</net.dinglisch.android.tasker.subbundled>
<net.dinglisch.android.tasker.subbundled-type>java.lang.Boolean</net.dinglisch.android.tasker.subbundled-type>
</Vals>
</Bundle>
<Str sr="arg1" ve="3">com.mobizsystems.mdm</Str>
<Str sr="arg2" ve="3">com.mobizsystems.mdm.ForceStopActivity</Str>
<Int sr="arg3" val="0"/>
</Action>
</Task>
</TaskerData>