dt-bindings: regulator: remove regulator pull-down support for stpmic1

Regulator high pull down are enabled by default so remove support in the
driver.
Signed-off-by: Pascal Paillet <p.paillet@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/st,stpmic1-regulator.txt

@@ -23,8 +23,6 @@ Switches are fixed voltage regulators with only enable/disable capability.
 Optional properties:
 - st,mask-reset: mask reset for this regulator: the regulator configuration
   is maintained during pmic reset.
-- regulator-pull-down: enable high pull down
-  if not specified light pull down is used
 - regulator-over-current-protection:
     if set, all regulators are switched off in case of over-current detection
     on this regulator,