Don't create withres-withoutdex files for R8

The withres-withoutdex files were added in b/195558228 because D8
produced errors when given an input jar that contained both class
and dex files:
Error: com.android.tools.r8.internal.Cc: Cannot create android app from an archive 'out/soong/.intermediates/libcore/libcore-crypto-tests/android_common/withres/libcore-crypto-tests.jar' containing both DEX and Java-bytecode content

It turns out R8 doesn't have this problem, it defaults to ignoring *.dex
files unless the com.android.tools.r8.allowDexInputToR8 system property
is set.  Remove the withres-withoutdex files when using R8, but keep
it in place for D8 for now.

Bug: 302573555
Bug: 303264288
Bug: 303064127
Test: m checkbuild
Test: m Calendar && m Calendar
Test: m framework-minus-apex && m framework-minus-apex
Change-Id: Ib6410f7fef6faf5913476c6423cdd27215c68c45