Bluetooth device slice improvement

- remove "Pair new device" row
- change the on/off toggle to a plus button for pairing new device
- roll back the title "Bluetooth devices"

Bug: 149667096
Test: robotest
Change-Id: I47e9c47b2ab0adacdbdbde34522d7c0172adda75
Merged-In: I47e9c47b2ab0adacdbdbde34522d7c0172adda75
(cherry picked from commit 5e462a852b)

tests/robotests/src/com/android/settings/testutils/SliceTester.java

@@ -242,16 +242,6 @@ public class SliceTester {
         assertThat(hasText(sliceItems, title, HINT_TITLE)).isTrue();
     }
 
-    /**
-     * Assert no slice item contains title.
-     *
-     * @param sliceItems All slice items of a Slice.
-     * @param title Title for asserting.
-     */
-    public static void assertNoSliceItemContainsTitle(List<SliceItem> sliceItems, String title) {
-        assertThat(hasText(sliceItems, title, HINT_TITLE)).isFalse();
-    }
-
     /**
      * Assert any slice item contains subtitle.
      *