[cmake] fix link issues of unit tests (#5309)
[cmake] fix link issues of unit tests (#5309)

I think openthread-ncp-ftd is added to unit tests' link libraries by
mistake. It's not required and as it depends on OT_PLATFORM, it would
cause openthread-simulation linked in unit test executables, which
would lead to a redefinition as some methods are defined in
test-platform.cpp.
chshu/openthread,chshu/openthread,bukepo/openthread,openthread/openthread,chshu/openthread,jwhui/openthread,srickardti/openthread,openthread/openthread,chshu/openthread,abtink/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,openthread/openthread,abtink/openthread,chshu/openthread,abtink/openthread,jwhui/openthread,bukepo/openthread,jwhui/openthread,chshu/openthread,bukepo/openthread,srickardti/openthread,abtink/openthread,srickardti/openthread,bukepo/openthread