Avoid loading the full file to memory in ConfigUpdateInstallReceiver

The conversation action model file is around 3MB, it may be a problem
to load the entire file into the memory in some low-end devices.

Test: 1. Testing all textclassifier models update from end to end
   adb shell rm -rf /data/misc/textclassifier/
   adb shell pm clear com.google.android.configupdater
   adb shell am broadcast  -a com.google.android.configupdater.GSERVICES_CHANGED -p "com.google.android.configupdater"
   adb shell dumpsys textclassification, observe all the files are there

BUG: 133808606
Change-Id: I720154dd35a2d58216d1bb65976c66cc0be5a9c7