browser-tweaks: remove browser.send_pings (#865)

It defaults to false already and is not necessary here.

Closes #686

_includes/sections/browser-tweaks.html

@@ -37,9 +37,6 @@ <h3>Getting started:</h3>
   <dt>browser.safebrowsing.phishing.enabled = false</dt>
   <dd>Disable Google Safe Browsing and phishing protection. Security risk, but privacy improvement.</dd>
 
-  <dt>browser.send_pings = false</dt>
-  <dd>The attribute would be useful for letting websites track visitors' clicks.</dd>
-
   <dt>browser.sessionstore.max_tabs_undo = 0</dt>
   <dd>Even with Firefox set to not remember history, your closed tabs are stored temporarily at Menu -&gt; History -&gt; Recently Closed Tabs.</dd>