chore(install): remove new tab page wallpaper preference

This commit removes the user preference for enabling the New Tab page wallpaper in the installation script.

install.ps1

@@ -77,11 +77,7 @@ Get-ChildItem -Path $firefoxProfilesPath | ForEach-Object {
         [PSCustomObject]@{
             "line"  = "user_pref(`"toolkit.telemetry.enabled`", false);"
             "desc"  = "Enable telemetry (disabled by default)"
-        },
-        [PSCustomObject]@{
-            "line"  = "user_pref(`"browser.newtabpage.activity-stream.newtabWallpapers.enabled`", true);"
-            "desc"  = "Enable New Tab page Wallpaper"
-        }
+        } 
     )
 $fileContent = @"
 user_pref("toolkit.legacyUserProfileCustomizations.stylesheets", true);