dt-bindings: i2c: renesas,i2c: Drop "renesas,i2c-rcar"

The compatible value "renesas,i2c-rcar" was deprecated in commit
ad4a8dc3 ("i2c: rcar: Add per-Generation fallback bindings"),
and never had any users in upstream Linux.  Drop its description from
the DT bindings.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>