manual: remove "Writing Nix Expressions" chapter

it is out of date, all over the place in level of detail, is really
about `nixpkgs`, and in general instructions should not be part of
a reference manual.

also:
- update redirects and internal links
- use "Nix language" consistently

1 files changed, 0 insertions, 16 deletions

diff --git a/doc/manual/src/expressions/builtins-prefix.md b/doc/manual/src/expressions/builtins-prefix.md
deleted file mode 100644
index c631a8453..000000000
--- a/doc/manual/src/expressions/builtins-prefix.md
+++ /dev/null
@@ -1,16 +0,0 @@
-# Built-in Functions
-
-This section lists the functions built into the Nix expression
-evaluator. (The built-in function `derivation` is discussed above.)
-Some built-ins, such as `derivation`, are always in scope of every Nix
-expression; you can just access them right away. But to prevent
-polluting the namespace too much, most built-ins are not in
-scope. Instead, you can access them through the `builtins` built-in
-value, which is a set that contains all built-in functions and values.
-For instance, `derivation` is also available as `builtins.derivation`.
-
-<dl>
-  <dt><code>derivation <var>attrs</var></code>;
-      <code>builtins.derivation <var>attrs</var></code></dt>
-  <dd><p><var>derivation</var> is described in
-         <a href="derivations.md">its own section</a>.</p></dd>