Remove confusing code introduced in 8fc4291e

Remove confusing code introduced in 8fc4291e

<ilmari> but why is $dump_str declared outside dump_value?
<ribasushi> ilmari: silly minimalistic microoptimization (not to reclear the dump every time it's needed)
<ribasushi> ilmari: my $foo { reuse $foo many time in this scope } *minimally faster* than { use my $foo_to_be_cleared_any_time_we_leave_scope }
<ribasushi> less for the scope unwinder to do
<ribasushi> as I said - it's silly, and 100% undetectable
<ilmari> is dump_value that hot?
<ribasushi> it's not hot at all
<ilmari> we've probably wasted more time discussing this now than the total CPU time saved by that micro-optimisation, over the entire future lifetime of DBIC
<ribasushi> ilmari: well, my 1st sentence today was admitting exactly that ;)
<ribasushi> I have been working on the rowparser for 5 days, the mindset is different, and it "bleeds through"