rm explicit keyword introduced by backporting another change

--HG--
branch : 3.2
Bug 920: fix compilation issue with MSVC 2015

--HG--
branch : 3.2
Bug 920: fix MSVC 2015 compilation issues

--HG--
branch : 3.2
extra : source : c3b9631dd1ebc4f3959a92a6c7bf017087e7d332