scripts: ipkg-remove: handle existing .ipk files without SourceName field

scripts: ipkg-remove: handle existing .ipk files without SourceName field

Package archives built before commit e6bcf1e4ac
("build: add ABI_VERSION to binary package names") lack the SourceName
control file field which caused ipkg-remove to skip such archives.

Add fallback code that matches the files by their basename followed by
an underscore, similar to how the old cleanup code worked.

Fixes: #2067
Signed-off-by: Jo-Philipp Wich <[email protected]>