meson: remove dummy_cpp

meson has gotten pretty smart about tracking C and C++ dependencies
(internal and external), and using the right linker. This wasn't always
the case and we created empty c++ files to force the use of the c++
linker. We don't need that any more.

Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
4 files changed