build: remove Cflags options from tests/CMakeLists.txt
build: remove Cflags options from tests/CMakeLists.txt

In commit 579b0ced6104a5b5cb0ba8f6d7220b568c1db3b6, Cflags were added to
tests/CMakeLists.txt. This overwrites the Cflag that are set from the
top-level makefile.
passing "-D Release" or "-D Debug" to cmake didn't worked anymore as
expected, because the cflags were overwritten.

rtrlib/rtrlib,rtrlib/rtrlib,rtrlib/rtrlib