ash: revert previous implementation of "A=1 A=2 B=$A cmd" code

ash: revert previous implementation of "A=1 A=2 B=$A cmd" code

Reverts this:

    commit 0e6f661e23d358cca104c24f8438d0ec64df32f1
    Date:   Fri Feb 15 15:02:15 2008 +0000
    ash: handle "A=1 A=2 B=$A; echo $B". closes bug 947.

A different fix from upstream has been imported by previous six commits.

Last seven commits, cumulative:

function                                             old     new   delta
poplocalvars                                           -     314    +314
mklocal                                                -     288    +288
pushlocalvars                                          -      48     +48
evalcommand                                         1372    1408     +36
unwindlocalvars                                        -      22     +22
ash_main                                            1022    1029      +7
setvar                                               167     172      +5
localvar_stack                                         -       4      +4
setvareq                                             303     302      -1
evalcase                                             271     269      -2
subevalvar                                          1202    1198      -4
localvars                                              4       -      -4
cmdenviron                                             4       -      -4
expandarg                                            984     973     -11
evalvar                                              589     574     -15
argstr                                              1164    1141     -23
dotcmd                                               335     303     -32
bltinlookup                                           51       5     -46
varvalue                                             709     596    -113
evalfun                                              456     270    -186
localcmd                                             364      44    -320
------------------------------------------------------------------------------
(add/remove: 5/2 grow/shrink: 3/11 up/down: 724/-761)         Total: -37 bytes
   text	   data	    bss	    dec	    hex	filename
 915353	    485	   6888	 922726	  e1466	busybox_old
 915320	    485	   6880	 922685	  e143d	busybox_unstripped

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