Symbols: resize the syms array when removing NoSymbol

On OpenBSD, with malloc_conf=S, the recallocarray() code detects a
size mismatch in ResizeKeyGroup when numLevels[group] doesn't match
the allocated size of syms[group].

Should fix xorg/app/xkbcomp#25



Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
Part-of: <xorg/app/xkbcomp!24>