Remove portable=true build flag

On the Raspberry Pi, which is currently our only production deployment,
the default scrcpy_server path is correct.

When we get around to deploying scrcpy on a NUC, we can deploy the
server to the default path, regardless of where `snap` would have
installed it.

mobot.mk

@@ -35,7 +35,6 @@ build-app: $(AVLIBS)
 		meson build-app --buildtype release --strip -Db_lto=true \
 		-Dlocal_libav=$(AVDIR) \
 		-Dcompile_server=false \
-		-Dportable=true \
 		|| (ret=$$?; rm -rf $@ && exit $$ret)
 
 scrcpy: build-app