[nrf fromtree] samples: net: zperf: Remove fixed size config for nRF70

nRF70 now by default uses variale buffers.

Signed-off-by: Chaitanya Tata <[email protected]>
(cherry picked from commit 8fe1df6)

Author: krish2718

samples/net/zperf/boards/nrf7002dk_nrf5340_cpuapp.conf

@@ -3,7 +3,6 @@ CONFIG_NET_PKT_RX_COUNT=28
 CONFIG_NET_PKT_TX_COUNT=27
 CONFIG_NET_BUF_RX_COUNT=28
 CONFIG_NET_BUF_TX_COUNT=54
-CONFIG_NET_BUF_DATA_SIZE=1100
 CONFIG_NRF70_MAX_TX_AGGREGATION=4
 CONFIG_NRF70_QSPI_LOW_POWER=n