Drop compatibility with pre 2012 adb clients

On very old versions of adb, when "adb bugreport" was executed,
the command "adb shell dumpstate" was run. This was later changed
to "adb shell bugreport". Change
1e339878 added a backwards
compatibility hack (see bug 6391938).

It turns out that nobody has been able to execute
/system/bin/dumpstate as a non-root user for 2 releases now due
to SELinux restrictions, so maintaining the code bloat to support
this workaround is pointless.

Delete the code.

Bug: 6391938
Change-Id: I49eebcca1fcec5a39593c53e2e6d23ec87f65a35