ath6kl: Remove the unused node table implementation

Now that the scan results are reported directly to the cfg80211 BSS
table there is no need for maintaining this internal node table
implementation for scan results. Remove the definitions and node
table functions.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>