For #469: remove "Your" from "Your library" string

(see https://github.com/mozilla-mobile/fenix/issues/469#issuecomment-480400794)

app/metrics.yaml

@@ -72,7 +72,7 @@ events:
       item:
         description: >
           A string containing the name of the item the user tapped. These items include:
-          Settings, Your library, Help, Desktop Site toggle on/off, Find in Page, New Tab,
+          Settings, Library, Help, Desktop Site toggle on/off, Find in Page, New Tab,
           Private Tab, Share, Report Site Issue, Back/Forward button, Reload Button
     bugs:
     - 1024

app/src/main/res/values/strings.xml

@@ -44,7 +44,7 @@
     <!-- Browser menu button that opens the settings menu -->
     <string name="browser_menu_settings">Settings</string>
     <!-- Browser menu button that opens a user's library -->
-    <string name="browser_menu_library">Your library</string>
+    <string name="browser_menu_library">Library</string>
     <!-- Browser menu toggle that requests a desktop site -->
     <string name="browser_menu_desktop_site">Desktop site</string>
     <!-- Browser menu button that opens the find in page menu -->