Fixing trivial warnings spotted by Mingw-2.0.0/gcc-3.2:

plink.c:65: warning: `password' defined but not used
(introduced in 1.50 [r1525])

[originally from svn r2332]
[r1525 == 466b1c82d5]

plink.c

@@ -62,8 +62,6 @@ void cmdline_error(char *p, ...)
     exit(1);
 }
 
-static char *password = NULL;
-
 HANDLE inhandle, outhandle, errhandle;
 DWORD orig_console_mode;