Remove special-case logic for running tests on host machines

I'm not sure what process sjg@ was using, but using CHECKDIR=${.OBJDIR} with
"make check" on ^/head is the correct thing to do. This unbreaks "make check"
for me (unsandboxed, not using CHECKDIR=${.OBJDIR}).

While here, fix a whitespace nit with LIBADD.

MFC after:	1 week

lib/libxo/tests/Makefile

@@ -242,13 +242,8 @@ PROGS+= test_11
 
 CFLAGS+=	-I${LIBXOSRC}/libxo -I${.CURDIR:H}
 
-LIBADD=		xo util 
+LIBADD=		xo util
 
 SUBDIR+=	encoder
 
-.if ${MACHINE} == "host"
-# make it easy to test without install
-TESTSDIR=	${.OBJDIR}
-.endif
-
 .include <bsd.test.mk>