BUILD: cfgparse: keep a single "curproxy"

BUILD: cfgparse: keep a single "curproxy"

Surprisingly, commit 00e00fb42 ("REORG: cfgparse: extract curproxy as a
global variable") caused a build breakage on the CI but not on two
developers' machines. It looks like it's dependent on the linker version
used. What happens is that flt_spoe.c already has a curproxy struct which
already is a copy of the one passed by the parser because it also needed
it to be exported, so they now conflict. Let's just drop this unused copy.