nativesdk: Clear TUNE_FEATURES

Similarly to what native.bbclass does, clear TUNE_FEATURES since these
aren't appropriate to the nativesdk build. This saves us having to change
down signature issues due to data in this variable.

(From OE-Core rev: 394c1bb8c8148d65b6188586fd4b6d8edc39ab88)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 2e5079e434504a3a22b609f7ddbb7f4c533c4cdb)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/nativesdk.bbclass

@@ -55,6 +55,7 @@ TARGET_CXXFLAGS = "${BUILDSDK_CXXFLAGS}"
 TARGET_LDFLAGS = "${BUILDSDK_LDFLAGS}"
 TARGET_FPU = ""
 EXTRA_OECONF_GCC_FLOAT = ""
+TUNE_FEATURES = ""
 
 CPPFLAGS = "${BUILDSDK_CPPFLAGS}"
 CFLAGS = "${BUILDSDK_CFLAGS}"