So, equipment trick (shield) first gives this ability:
Hurl Shield (Throw Anything): You can throw your shield as a ranged improvised weapon. You must be holding (not wearing) your shield to perform this trick. If you are using a throwing shield, there is no reason to use this trick.
Notice that it is redundant for throwing shields, and called out as such.
Then it gives this ability:
Ricochet Shield (Deadly Aim, Throw Anything): When you throw a shield, you can bounce it off one or more hard surfaces in order to strike a target from an unexpected angle or to bypass an obstacle such as cover. Each object you ricochet your shield off of imposes a –2 penalty on the attack roll. Range increments apply for the total distance the shield travels, not just the direct distance between you and the target.
Now while it does not say that a throwing shield is exempt from the throw anything portion of the requirement, would you find it reasonable? Do you find requiring throw anything to throw a shield specifically exempted from the need for throw anything a few sentences ago reasonable?
From the RAW side everything is clear.
To hurl a shield you can use a special ability ('Hurl Shield') or you use a special shield. 'Ricochet Shield' is another ability that has its own prerequisites. Neither 'Hurl Shield' or a throwing shield are mentioned as prerequites or as replacement for the prerequisites.
Is the prerequisite 'Throw Anything' redundant ? Yes i think so but then it is a housrule.
Should a throwing shield replace the prerequisite 'Throw Anything' for 'Ricochet Shield' ? Yes i would allow it but again then it is a houserule.