[C++] Remove explicit appending of `-g` flag.
[C++] Remove explicit appending of `-g` flag.

This flag is automatically appended by CMake in debug builds which
include RelWithDebInfo. Release mode should not have debug symbols.

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