chan_dahdi: Fix unable to get index warning when transferring an analog call.

Transferring an analog call using flashhooks generated an unable to get
index WARNING message when the transfer is completed.

* Removed unnecessary analog subchannel shell games when transferring a
call using flashhooks.

Thanks to Tzafrir Cohen for mentioning this in a comment on issue
ASTERISK-22720.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@401378 f38db490-d61c-443f-a65b-d21fe96a405b