gdbserver/Windows: Rely purely on event info when handling DLL load event

gdbserver/Windows: Rely purely on event info when handling DLL load event

This is the GDBserver counterpart of a change we recently made in
GDB to only rely on get_image_name to determine its name.

This simplification, in turn, allows us to remove a fair amount of
functions and globals which now become unused.

gdb/gdbserver/ChangeLog:

	* win32-low.c (psapi_get_dll_name,
	* win32_CreateToolhelp32Snapshot): Delete.
	(win32_CreateToolhelp32Snapshot, win32_Module32First)
	(win32_Module32Next, load_toolhelp, toolhelp_get_dll_name):
	Delete.
	(handle_load_dll): Add function description.
	Remove code using psapi_get_dll_name and toolhelp_get_dll_name.