dumpstate: call printflags instead of reading flag files explicitly

Now that the printflags device tool exists, dumpstate no longer needs to
read the aconfig files itself. Teach dumpstate to call printflags
instead.

As a bonus, printflags will also include the current flag values as
defined by device_config.

Bug: 302452801
Test: adb bugreport /tmp/bugreport.zip && unzip -c /tmp/bugreport.zip bugreport*.txt | grep --text -A20 -e 'ACONFIG FLAGS'
Change-Id: I6be4aab8dad6e08d2bc0e646224b3682927e34a2