qcacld-3.0: Remove csr_is_infra_connected()
Change I2b469c6cb2e6bdfc735b04e9bd6f12ba0d41fea4 ("qcacld-3.0: Remove
sme_is_sta_p2p_client_connected()") removed the last client of
csr_is_infra_connected(). Since the function is now obsolete, remove
it.
Change-Id: I5a71cad7414aee56a981e640ef66687fe0433b4f
CRs-Fixed: 2371135