config: remove unneeded struct field

As well as receiving the config key and value, config callbacks also receive a "struct key_value_info" containing information about the source of the key-value pair. Accessing the "path" field of this struct from a callback passed to repo_config() results in a use-after-free. This happens because repo_config() first populates a configset by calling config_with_options() and then iterates over the configset with the callback passed by the caller. When the configset is constructed it takes a shallow copy of the "struct key_value_info" for each config setting. This leads to the use-after-free as the "path" member is freed before config_with_options() returns. We could fix this by interning the "path" field as we do for the "filename" field but the "path" field is not actually needed. It is populated with a copy of the "path" field from "struct config_source". That field was added in d14d42440d8 (config: disallow relative include paths from blobs, 2014-02-19) to distinguish between relative include directives in files and those in blobs. However, since 1b8132d99d8 (i18n: config: unfold error messages marked for translation, 2016-07-28) we can differentiate these by looking at the "origin_type" field in "struct key_value_info". So let's remove the "path" members from "struct config_source" and "struct key_value_info" and instead use a combination of the "filename" and "origin_type" fields to determine the absolute path of relative includes. Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>