Remove unnecessary invokation on AppSearch

There are some legacy logic which attempts to load shortcuts from xml
file, which in most cases ended up calling AppSearchSession#putDocuments
with an empty list because there are nothing to write into AppSearch.
Since this is happening for every package that has a shortcut, these
invokations collectively added some delay when launcher is starting.
This CL removes the invokations altogether since they are not needed in
the first place.

Bug: 183982287
Test: flash the device, reboot and observe
Test: atest ShortcutManagerTest1 ShortcutManagerTest2
ShortcutManagerTest3 ShortcutManagerTest4 ShortcutManagerTest5
ShortcutManagerTest6 ShortcutManagerTest7 ShortcutManagerTest8
ShortcutManagerTest9 ShortcutManagerTest10 ShortcutManagerTest11
Test: atest CtsShortcutManagerTestCases

Change-Id: I57bd9ed93c1a2068a090ff3d67906702481220fd