[C++] Remove explicit appending of version flags.
[C++] Remove explicit appending of version flags.

CMake automatically appends these when it detects CMAKE_C_STANDARD and
CMAKE_CXX_STANDARD has been set.

real-logic/Aeron,galderz/Aeron,real-logic/Aeron,galderz/Aeron,EvilMcJerkface/Aeron,galderz/Aeron,real-logic/Aeron,galderz/Aeron,EvilMcJerkface/Aeron,mikeb01/Aeron,mikeb01/Aeron,real-logic/Aeron,mikeb01/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,EvilMcJerkface/Aeron