Remove deprecated constructs from Libdoc spec files

[pekkaklarck]

datatypes were deprecated in favor of more generic typedocs in RF 5.0 (#4160) and in RF 6.1 there were argument type related changes (#4538). We have preserved old data in specs for backwards compatibility reasons but now it's time remove it. The main motivation is making specs simpler and smaller.

Libdoc can read old specs. That support can still be preserved.

[pekkaklarck]

Small changes, such as updating schema versions, still needed.

[pekkaklarck]

It actually seems deprecated constructs were only removed from schemas. They still need to be removed from spec files themselves.

[pekkaklarck]

I try to list here everything that is removed as part of this issue:

• <datatypes> section isn't written anymore to XML specs. It was deprecated in favor of <typedocs> already in RF 5.0 (Libdoc: Include automatic argument conversion info #4160).
• datatypes isn't written to JSON spec either and typedocs should be used instead. See the issue referenced above for more info. This removal was done in 460fb10 but it was accidentally linked to a wrong issue.
• Type name isn't anymore written to XML specs as content of <type> elements. It has been available in name attribute of <type> elements since RF 6.1 (Libdoc doesn't handle parameterized types like list[int] properly #4538).
• types and typedocs attributes have been removed from arguments in JSON specs. The type attribute introduced in RF 6.1 (Libdoc doesn't handle parameterized types like list[int] properly #4538) needs to be used instead.
• Removed constructs have been removed also from Libdoc schema files.