Remove duplicate packages by running in `target/linux/` rather than
`target/linux/<target>/<subtarget>` and sort packages alphabetically.
Squash commit of:
7880a64848 build,json: 3rd fixup of default_packages
b36068d35d build,json: fixup fixup of arch_packages
1bf2b3fe90 build,json: fixup missing arch_packages
Signed-off-by: Paul Spooren <mail@aparcar.org>