debug/elf: fix offset for GNU version symbols
debug/elf: fix offset for GNU version symbols

Since we no longer skip the first entry when reading a symbol table,
we no longer need to allow for the offset difference when processing
the GNU version symbols.

Unbreaks builds on Linux.

R=golang-dev, agl, iant
CC=golang-dev
http://codereview.appspot.com/6843057

tv42/old-go,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,apparentlymart/golang,dsriram/golang,tv42/old-go,apparentlymart/golang,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,tv42/old-go,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang