common : remove common_has_curl() (#16351)

`test-arg-parser.cpp` has been updated to work consistently,
regardless of whether CURL or SSL support is available, and
now always points to `ggml.ai`.

The previous timeout test has been removed, but it can be
added back by providing a dedicated URL under `ggml.ai`.

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

common/arg.cpp

@@ -266,10 +266,6 @@ static std::string read_etag(const std::string & path) {
 
 #ifdef LLAMA_USE_CURL
 
-bool common_has_curl() {
-    return true;
-}
-
 //
 // CURL utils
 //
@@ -585,10 +581,6 @@ std::pair<long, std::vector<char>> common_remote_get_content(const std::string &
 
 #else
 
-bool common_has_curl() {
-    return false;
-}
-
 struct common_url {
     std::string scheme;
     std::string user;