BUG/MEDIUM: config: don't pick unset values from last defaults section

BUG/MEDIUM: config: don't pick unset values from last defaults section

Since commit 1.3.14 with commit 1fa3126ec ("[MEDIUM] introduce separation
between contimeout, and tarpit + queue"), check_config_validity() looks
at the last defaults section to update all proxies' queue and tarpit
timeouts if they were not set!

This was apparently an attempt to properly set them on the fallback values,
except that the fallback values were taken from the default proxy before
looking at the current proxy itself. The worst part of it is that it might
have randomly worked by accident for some configurations when there was a
single defaults section, but has certainly caused too short queue
expirations once another defaults section was added later in the file with
these explicitly defined.

Let's remove the defproxy part and keep only the curproxy ones. This could
be backported everywhere, the bug has been there for 13 years.