dt-bindings: clock: drop obsolete stericsson,abx500.txt

These bindings are already (better) described in mfd/stericsson,ab8500.yaml,
drop these now obsolete bindings.

Signed-off-by: Stanislav Jakubek <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Reviewed-by: Krzysztof Kozlowski <[email protected]>
Link: https://lore.kernel.org/r/Zm7I2Zbq1JNPoEJp@standask-GA-A55M-S2HP
Signed-off-by: Rob Herring (Arm) <[email protected]>

Author: Stanislav Jakubek