Remove search configuration

[cketti]

Fixes an ANR reported via Google Play.

This Binder call may be taking too long, causing the main thread to wait, and triggering the ANR
      at android.os.BinderProxy.transact (BinderProxy.java:584)
      at android.app.ISearchManager$Stub$Proxy.getSearchableInfo (ISearchManager.java:201)
      at android.app.SearchManager.getSearchableInfo (SearchManager.java:864)
      at com.fsck.k9.activity.MessageList.initializeSearchMenuItem (MessageList.kt:923)
Your app's code results in the Binder call above. Code that triggers Binder calls should be moved out of the main thread.
      at com.fsck.k9.activity.MessageList.onCreateOptionsMenu (MessageList.kt:907)

The search key now no longer opens the Search activity from anywhere in the app. Pressing the search key while the message list is displayed, will expand and focus the search view in the toolbar (can be triggered using adb shell input keyevent 84).

[wmontwe]

LGTM