Remove as_root calls from the printf testsuite

Remove as_root calls from the printf testsuite

Once upon a time, we would use sudo staprun, and so output files from
"-o" were owned by root.  For a while now we've used a setuid staprun
instead, and the output files are created by stapio as the user.  Thus,
we don't need as_root to remove those files anymore.

* testsuite/systemtap.printf/end1b.exp: Clean up without as_root.
* testsuite/systemtap.printf/mixed_outb.exp: Ditto.
* testsuite/systemtap.printf/out1b.exp: Ditto.
* testsuite/systemtap.printf/out2b.exp: Ditto.
* testsuite/systemtap.printf/out3b.exp: Ditto.