Keep the logging library out of this low-level libcurl wrapper.

Similar to commits 1686f4e8 and
30a5dd26

Our Windows build is built with `--disable-netrc`, and that makes
CURLOPT_NETRC fail, causing failures with all streams.  D'oh!

Closes https://github.com/MusicPlayerDaemon/MPD/issues/886

Apparently, it's not possible to change CURLOPT_NETRC on Android.

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Prevents compiling those sources many times, once for each debug
program using it.

This reverts commit 4475b8ca.  Further
testing revealed that the threaded resolver still uses a timeout of
0ms.  This revert however lowers the bound to a minimum of 1ms instead
of 10ms.

curl_multi_remove_handle() calls our socket function, and there's no
need to call curl_multi_socket_action().

This was a problem 9 years ago, and apparently, it has been fixed long
ago.

For simplicity, this commit removes a workaround for an old CURL bug.