Remove B_PROT_* and related code

Use standard error codes instead.
This allows using error code returned by the underlying functions
directly, and makes it possible to use strerror for debugging. So, we
can also remove StatusString() from the various *Request classes.

headers/os/net/HttpRequest.h

@@ -49,7 +49,6 @@ public:
 
 			status_t			Stop();
 			const BUrlResult&	Result() const;
-			const char*			StatusString(status_t threadStatus) const;
 
 	static	bool				IsInformationalStatusCode(int16 code);
 	static	bool				IsSuccessStatusCode(int16 code);
@@ -123,13 +122,6 @@ private:
 			bool				fOptAutoReferer : 1;
 };
 
-// ProtocolLoop return status
-enum {
-	B_PROT_HTTP_NOT_FOUND = B_PROT_THREAD_STATUS__END,
-	B_PROT_HTTP_THREAD_STATUS__END
-};
-
-
 // Request method
 const char* const B_HTTP_GET = "GET";
 const char* const B_HTTP_POST = "POST";