bc: remove "error ids": serve no useful purpose, error message should be explanatory...

bc: remove "error ids": serve no useful purpose, error message should be explanatory enough

function                                             old     new   delta
bc_warn_fmt                                           17      14      -3
bc_err_fmt                                            15      12      -3
bc_vm_posixError                                     205     189     -16
bc_vm_error                                          156     138     -18
bc_errs                                               28       -     -28
bc_err_ids                                            58       -     -58
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 0/4 up/down: 0/-126)           Total: -126 bytes
   text	   data	    bss	    dec	    hex	filename
 988288	    485	   7296	 996069	  f32e5	busybox_old
 988122	    485	   7296	 995903	  f323f	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>