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

Package archives built before commit e6bcf1e4
("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 <jo@mein.io>

scripts/ipkg-remove

@@ -10,6 +10,11 @@ for pkg in "$@"; do
 			break
 		fi
 	done
+	case "$pkg" in
+		*/"${sourcename}_"*.ipk)
+			rm -vf "$pkg"
+		;;
+	esac
 done
 
 exit 0