[Ravenwood] Faster framework-minus-apex processing

It turned out "API file" generation was rather slow because
this file's content isn't actually fully sharded.

Let's only generate any of the *.txt and *.csv files in _all.

Bug: 313930116
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh
Flag: EXEMPT host side test change only
Change-Id: Ic29b5aa81e5f9e269643c63a0acc5c21c0971ad3