libobs: Refactor check for Windows bitness/arch

Commit aa899c2 (PR #603) added logging for Windows bitness/arch, but it
was a bit incomplete/short-sighted.  It only added that information to
the regular logs.  This commit makes it easier to retrieve that
information for other purposes, like the crash handler.

libobs/obs-windows.c

@@ -172,16 +172,6 @@ static void log_available_memory(void)
 			note);
 }
 
-static bool is_64_bit_windows(void)
-{
-#if defined(_WIN64)
-	return true;
-#elif defined(_WIN32)
-	BOOL b64 = false;
-	return IsWow64Process(GetCurrentProcess(), &b64) && b64;
-#endif
-}
-
 static void log_windows_version(void)
 {
 	struct win_version_info ver;