Cygwin: stop handling files with .com suffix like .exe files

Cygwin: stop handling files with .com suffix like .exe files

.com is a remnant from the past.  There are only five executables
left:

  chcp.com
  format.com
  mode.com
  more.com
  tree.com

Calling them on the command line already requires to use the
suffix anyway.  So drop useless .com test from the execve test
for scripts (they are handled earlier in the same function
as executables) and do not handle them like .exe suffixes in
other functions.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>