qcacld-3.0: Remove csr_rates_find_best_rate()

Function csr_rates_find_best_rate() is unused, so remove it, along
with the now unused support function csr_rates_mac_prop_to_dot11().

Change-Id: I0a9e7894734a5a4f47030f8d12d0e41d0b23e95e
CRs-Fixed: 2361290
2 files changed