(detect_coding_iso2022, setup_coding_system): Remove

(detect_coding_iso2022, setup_coding_system): Remove
unused variable `i'.
(detect_coding_mask): Remove unused variable `idx'.
(detect_coding): Remove unused variable `i'.
(ccl_coding_driver): Remove unused variable `result'.
(run_pre_post_conversion_on_str): Remove unused variable `prev'.
(decode_coding_string): Remove unused variables `to' and
`gcpro1'.
(encode_coding_string): Remove unused variables `gcpro1' and
`saved_coding_symbol'.
(Ffind_coding_systems_region_internal): Remove function-local
variable args[], leave only the block-local one.
(code_convert_region1): Remove unused variable `len'.