[cmyth] cosmetics: Remove dummy code

Since i reviewed the live TV chain code few months ago, a chain entry cannot be incomplete. So a valid chain entry is added in one pass.
Removes chain_add_url, chain_add_file and chain_add_prog.
[cmyth] Memory leak on failure
[cmyth] Memory leak

Introduced in commit e9fab002b9dc981f2862de820d2f8952cf256bf1 in cmyth_livetv_chain_seek().

Resolution: Set 'ret' and goto 'out:' instead return.