NFC: st21nfcb: remove st21nfcb_nci_i2c_disable

ndlc_remove already calls st21nfcb_nci_i2c_disable and
phy->powered is already set to 0.

Cc: stable@vger.kernel.org
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>