[fenix] For https://github.com/mozilla-mobile/fenix/issues/4487 Set activity title only once in Bookmark fragment

Removed label from nav_graph that caused label to be set for each navigation
Removed title setting in onCreate() called for each navigation
Changed logic for checking current root when setting UI for normal mode

app/src/main/java/org/mozilla/fenix/library/bookmarks/BookmarkFragment.kt

@@ -120,7 +120,6 @@ class BookmarkFragment : LibraryPageFragment<BookmarkNode>(), BackHandler {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        activity?.title = getString(R.string.library_bookmarks)
         setHasOptionsMenu(true)
     }
 

app/src/main/java/org/mozilla/fenix/library/bookmarks/BookmarkView.kt

@@ -150,7 +150,7 @@ class BookmarkView(
 
     private fun setUiForNormalMode(root: BookmarkNode?) {
         super.setUiForNormalMode(
-            if (BookmarkRoot.Mobile.matches(root)) context.getString(R.string.library_bookmarks) else root?.title,
+            if (BookmarkRoot.Mobile.id == root?.guid) context.getString(R.string.library_bookmarks) else root?.title,
             view.bookmark_list
         )
     }

app/src/main/res/navigation/nav_graph.xml

@@ -255,7 +255,6 @@
     <fragment
         android:id="@+id/bookmarkFragment"
         android:name="org.mozilla.fenix.library.bookmarks.BookmarkFragment"
-        android:label="@string/library_bookmarks"
         tools:layout="@layout/fragment_bookmark">
         <argument
             android:name="currentRoot"