Fix some _validate_property not correctly refactored

[RedMser]

Some old code was checking for properties that used / for category separation, but now _ is used instead.

Found with regex: property\.name.+\/

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Also removed PROPERTY_USAGE_INTERNAL in _validate_property as this flag is only relevant for doctool, which only checks the property definition's usage flags.

Found with regex: property\.usage.+INTERNAL

[YuriSizov]

is it okay for the property usage to stay "NONE" instead of "NO_EDITOR"?

NO_EDITOR means it's not visible in the Inspector, but I guess in this case we don't want them to be serializable either. PROPERTY_USAGE_INTERNAL in there is likely a misuse though.

If a specific default value must be set regardless, there is also DEFVAL().

[RedMser]

PROPERTY_USAGE_INTERNAL in there is likely a misuse though.

9b8e8b2 split off INTERNAL from NO_EDITOR, so I assume they replaced this everywhere, even in places where it makes no difference.
The flag seems to only influence docs generation, which from what I can tell only reads the property definition's usage flags, so I assume this flag shouldn't be used here.
I removed all uses of INTERNAL inside of _validate_property as a 2nd commit, let me know if that's okay. (Find-and-replaced property\.usage.+INTERNAL regex and confirmed each result by hand)

If a specific default value must be set regardless, there is also DEFVAL().

Just found the API for it, thanks! I re-added it, since it's useful to see in the docs.

[YuriSizov]

I removed all uses of INTERNAL inside of _validate_property as a 2nd commit, let me know if that's okay. (Find-and-replaced property\.usage.+INTERNAL regex and confirmed each result by hand)

I guess it should be okay, because @reduz complained about it the other day.

[akien-mga]

Thanks!