Build warning fixes in WebProcessCurl.

Reviewed by: The Build.
Build warning fixes in WebCoreArgumentCodersCurl.
Remove unused paramter names from the method.

Reviewed by: The Build.
Build warning fixes in DownloadCurl file.
Removed unused parameter names from the methods.

Reviewed by: The Build.
Build warning fix in WebContextNix file.
Added UNUSED_PARAM in case soup is not used as network backend.

Reviewed by: The Build.