bug#21528: 25.0.50; gud tries to guess what file we're debugging, which can take a long time

[Dima Kogan]

Hi. Currently when the user invokes any gud-based mode ('M-x pdb' for
instance) the minibuffer pops up with a suggested command. This command
tries to guess what you're trying to debug based on some pretty
arbitrary heuristics. This is in 'gud-query-cmdline' in gud.el

These heuristics include looking at each file in the current directory
to find the most recent executable file. In my experience this almost
never is what I want. If I'm doing remote debugging with tramp and the
current directory has many files in it, then emacs can sit there for a
very long time before opening the minibuffer, while it looks at all the
files in the remote directory. I think this delay changes this behavior
from not-useful to harmful, and I think it should be removed. Thoughts?