Fix Proguard configuration output from R8 invocation

The output when using `--pg-conf-output` seems to be flaky. In the
meantime, use `-printconfiguration` to generate full config summaries
for each R8 invocation.

Bug: 281081834
Test: m && \
      find $ANDROID_BUILD_TOP/out -name proguard_configuration -empty
Change-Id: I0c8c36212e338b50505184076f4c470a5d3d9b94