Supporting logging to a file complicates upgrading helper code to use
debugs() because DebugFile code calls commSetCloseOnExec(), and our
comm/libminimal does not currently provide a functioning implementation
for that API: The existing implementation is an unconditional assert.
To save development time while upgrading helpers, we are dropping this
feature. It can probably be emulated using shell redirection tricks.

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Backport of PR squid-cache#1872

Co-authored-by: Amos Jeffries <[email protected]>