Revert "dt-binding: i2c: add bus-supply property"

This reverts commit 6aab46bc. Testing in
linux-next showed it needs some more time.
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/devicetree/bindings/i2c/i2c.txt

@@ -23,9 +23,6 @@ Optional properties (per bus)
 These properties may not be supported by all drivers. However, if a driver
 wants to support one of the below features, it should adapt these bindings.
 
-- bus-supply
-	phandle to the regulator that provides power to SCL/SDA.
-
 - clock-frequency
 	frequency of bus clock in Hz.