arm/gn: remove nativesdk

Building GN in a SDK environment isn't as trivial, as it needs to know
the target configuration it should inherit cross-canadian. Also, building
for mingw32 hosts breaks the build.

For now there's no immediate need for GN in nativesdk, so remove it.

Change-Id: I3b969639fa8ad7780c53ae2bc8a3f166773ee4b9
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm/recipes-devtools/gn/gn_git.bb

@@ -22,7 +22,6 @@ do_configure[cleandirs] += "${B}"
 do_configure() {
     python3 ${S}/build/gen.py \
         --platform=${TARGET_OS} \
-        --host=${HOST_OS} \
         --out-path=${B} \
         --no-strip
 }
@@ -36,4 +35,4 @@ do_install() {
     install ${B}/gn ${D}${bindir}
 }
 
-BBCLASSEXTEND = "native nativesdk"
+BBCLASSEXTEND = "native"