winpr/library: fix win32 test and some cleanup

winpr/library: fix win32 test and some cleanup

On Windows we seem to have to load the TestLibrary[AB] test libraries
from in same folder the test executable runs.

Also removed the empty RemoveDllDirectory, SetDefaultDllDirectories,
AddDllDirectory tests and the redundant FreeLibrary test.

TestLibrary now works and succeeds on Win32.

sadasd