fixed assigned but unused var warnings

[walf443]

When I run test my envrionement, some warnings occured.
This PR fixed this warnings.

install -c tmp/x86_64-darwin18/stackprof/2.6.1/stackprof.bundle lib/stackprof/stackprof.bundle
cp tmp/x86_64-darwin18/stackprof/2.6.1/stackprof.bundle tmp/x86_64-darwin18/stage/lib/stackprof/stackprof.bundle
/Users/yoshimin/src/github.com/tmm1/stackprof/test/test_stackprof.rb:151: warning: assigned but unused variable - raw
Run options: --seed 43865

# Running:

....................../Users/yoshimin/src/github.com/tmm1/stackprof/lib/stackprof/report.rb:45: warning: assigned but unused variable - addr
..

Finished in 0.307169s, 78.1329 runs/s, 244.1653 assertions/s.
24 runs, 75 assertions, 0 failures, 0 errors, 0 skips