gdbserver/win32: fix crash on detach

gdbserver/win32: fix crash on detach

this patch fixes a crash in gdbserver whenever a process is detached.
the crash is caused by `detach` calling `remove_process` before `win32_clear_inferiors`

error message:

Detaching from process 184
../../gdbserver/inferiors.cc:160: A problem internal to GDBserver has been detec
ted.
remove_process: Assertion `find_thread_process (process) == NULL' failed.

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

Approved-By: Tom Tromey <tom@tromey.com>