tests: remove .SECONDARY special target

tests: remove .SECONDARY special target

The special target should not be needed anymore, and caused (perhaps
due to a Make bug) a failure with "make -j2".  In any case, the
main makefile is a better place for such special targets rather
than an included makefile.

Reported-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>