Remove unnecessary crashpad:: qualification from implicit_cast<>
Remove unnecessary crashpad:: qualification from implicit_cast<>

This undoes 595803e1be18, a workaround that should no longer be
necessary now that base no longer provides implicit_cast<> in the global
namespace.

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1356673003 .

Chilledheart/crashpad,chromium/crashpad,chromium/crashpad,atom/crashpad,chromium/crashpad,Chilledheart/crashpad,Chilledheart/crashpad,atom/crashpad,atom/crashpad