Drop examples from closure language reference

Relates to #1929

The language reference should be focused on the language concepts, not describe how various commands make use of it, and especially not in the form of examples.

All these commands have closure examples in the docs comments. All listed commands link to their respective docs.

Dropping the examples increases focus of the *reference* doc, and reduces risks of doc duplication and of command changes leading to outdated lang ref docs.

Author: Kissaki

lang-guide/chapters/types/basic_types/closure.md

@@ -107,82 +107,3 @@ Closures are used in Nu extensively as parameters to iteration style commands li
 - [`upsert`](/commands/docs/upsert.md)
 - [`zip`](/commands/docs/zip.md)
 
-### Examples of using closures
-
-Here are a few select, concise examples to illustrate the broad use of closures with some of the aforementioned common Nushell commands:
-
-#### `each` – Applying a transformation
-
-The `each` command iterates over input, applying a closure to transform each item.
-
-```nu
-[1 2 3] | each { |num| $num * 10 }
-```
-
-_Explanation:_ This takes a list of numbers. The closure `{|num| $num * 10}` is executed for each number (`num`), multiplying it by 10.
-
-**Output:**
-
-```nu
-[10 20 30]
-```
-
----
-
-#### `where` – Filtering data
-
-The `where` command filters data based on a condition defined in a closure. The closure must return true (keep) or false (discard).
-
-```nu
-ls | where { |file_info| $file_info.size > 1mb }
-```
-
-_Explanation:_ This lists files and then filters them. The closure `{|file_info| $file_info.size > 1mb}` checks if each file's size is greater than 1 megabyte.
-
-**Output:**
-
-```nu
-# A table of files larger than 1MB
-```
-
-_Closure's role:_ Defines the operation to perform on every element.
-
----
-
-#### `sort-by` – Custom sorting logic
-
-The `sort-by` command sorts a list or table. The closure is used to extract or calculate the value to sort on for each item.
-
-```nu
-["kiwi" "apple" "banana"] | sort-by { |fruit_name| $fruit_name | str length }
-```
-
-_Explanation:_ This sorts a list of fruit names. The closure `{|fruit_name| $fruit_name | str length}` calculates the length of each fruit name. `sort-by` then uses these lengths for sorting.
-
-**Output:**
-
-```nu
-["kiwi" "apple" "banana"] # sorted by string length: kiwi (4), apple (5), banana (6)
-```
-
-_Closure's role:_ Specifies the attribute or derived value to use for comparison during sorting.
-
----
-
-#### `reduce` – Aggregating values
-
-The `reduce` command processes a list to accumulate a single result. The closure defines how to combine the current item with the accumulated value.
-
-```nu
-[1 2 3 4] | reduce { |accumulator, current_value| $accumulator + $current_value }
-```
-
-_Explanation:_ This sums the numbers in the list. The closure `{|current_value, accumulator| $accumulator + $current_value}` adds the `current_value` to the `accumulator`. By default, the first item is the initial accumulator, and iteration starts from the second.
-
-**Output:**
-
-```nu
-10
-```
-
-_Closure's role:_ Defines the operation for combining elements into a single accumulated value.