Remove -D_CRT_SECURE_NO_WARNINGS again.

No longer needed since strncpy is now exempt via #pragma.

I tested this by running cmake for VS2008, then loading CppUTest.sln into VS. I compiled the ALL_BUILD and RUN_TESTS targets, which build and run as expected. There are a lot of other targets, like "Nightly" and "Experimental" -- does anyone know how to use these?