windows: Remove use of WIN32_LEAN_AND_MEAN from crashdump.c.

Since 8162464a25 we do so in win32_port.h. But it likely didn't do much
before that either, because at that point windows.h was already included via
win32_port.h.

Reported-By: Tom Lane
Discussion: https://postgr.es/m/612842.1636237461@sss.pgh.pa.us

src/backend/port/win32/crashdump.c

@@ -38,8 +38,6 @@
 
 #include "postgres.h"
 
-#define WIN32_LEAN_AND_MEAN
-
 /*
  * Some versions of the MS SDK contain "typedef enum { ... } ;" which the MS
  * compiler quite sanely complains about. Well done, Microsoft.