[style] Remove underscores from gtest names in signature_algorithm_unittest.cc
[style] Remove underscores from gtest names in signature_algorithm_unittest.cc

Underscores are discouraged by gtest:
https://code.google.com/p/googletest/wiki/FAQ#Why_should_not_test_case_names_and_test_names_contain_underscore

BUG=None

Review URL: https://codereview.chromium.org/1249833006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#339974}

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