Do not generate copyable slices for Settings Search

Copyable slices is to provide user a quickly sub-text copying way on
Settings Search. Since we plan to remove all sub-text from Settings
Search, the copying feature is no longer available.

Therefore, we don't need to generate copyable slices in Settings
anymore.

Impact search result:
Build number, Phone number, Hardware version, Serial number and IMEI

Bug: 143118037
Test: visual and robotests
Change-Id: I81474aed994678c42d73cc59e169573880de1378

tests/robotests/src/com/android/settings/deviceinfo/BuildNumberPreferenceControllerTest.java

@@ -205,9 +205,4 @@ public class BuildNumberPreferenceControllerTest {
         final CharSequence data = clipboard.getPrimaryClip().getItemAt(0).getText();
         assertThat(data.toString()).isEqualTo(mController.getSummary());
     }
-
-    @Test
-    public void isPublicSlice_returnTrue() {
-        assertThat(mController.isPublicSlice()).isTrue();
-    }
 }