ShortcutManager: Floating shortcuts shouldn't have target activities.

Previously, even floating shortcuts (pinned but not dynamic nor
manifest) had target activities.  Now we're going to allow headless
apps to have pinned shortcuts, in which cases shortcuts won't have
target activities, let's just always remove target activities
from floating shortcuts.

Test: adb shell am instrument -e class com.android.server.pm.ShortcutManagerTest1 -w com.android.frameworks.servicestests
... to Test8.

Test: cts-tradefed run cts --skip-device-info --skip-preconditions --skip-system-status-check com.android.compatibility.common.tradefed.targetprep.NetworkConnectivityChecker -a armeabi-v7a -m CtsShortcutManagerTestCases
Test: cts-tradefed run cts --skip-device-info --skip-preconditions --skip-system-status-check com.android.compatibility.common.tradefed.targetprep.NetworkConnectivityChecker -a armeabi-v7a -m CtsShortcutHostTestCases

Change-Id: I10e5b87338cafb90e6566b3526f892c5330c73e9