docs: remove obsolete samples

[jskeet]

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 2 region tags.

• firestore/api/OrderLimitData/Program.cs:119, tag firestore_query_order_field_invalid
• firestore/api/QueryData/Program.cs:323, tag firestore_query_filter_range_invalid

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[jskeet]

Will wait until we've got absolute confirmation on this before merging.