Fix SearchFragment crash in tests.

Cause of crash: FragmentManager is already executing transactions.
This is because we unnecessarily resets the current query string,
indirectly invoking onQueryTextChange, causing a fragment transaction;
later when the searchView focus changes. it causes a second fragment
transaction. Fixes by removing the query reset step (it gets reset at
next expansion of search view anyway).

Bug: 182958870
Test: atest DocumentsUIGoogleTests
Change-Id: I21de9ec3a2e8c72be1d0ce7c7ccfd98a4567e2a5