PR29926: debuginfod: Fix usage of deprecated CURLINFO_*

PR29926: debuginfod: Fix usage of deprecated CURLINFO_*

The `CURLINFO_SIZE_DOWNLOAD_T` and `CURLINFO_CONTENT_LENGTH_DOWNLOAD_T`
identifiers are `enum`s, not pre-processor definitions, so the current
`#ifdef` logic is not selecting the newer API.  This results in the
older identifiers being used and they now generate errors when compiled
against Curl 7.87, which has silently deprecated them, causing GCC to
emit `-Werror=deprecated-declarations`.

Instead, the newer identifiers were added in Curl 7.55, so explicitly
check for `CURL_AT_LEAST_VERSION(7, 55, 0)` instead of the current
logic.  This eliminates the error when compiling against Curl 7.87.

Ref: https://github.com/curl/curl/pull/1511

Signed-off-by: Andrew Paprocki <andrew@ishiboo.com>