Revert "Improve declare_dependency() example in Generating-sources.md [skip ci]"

This reverts commit 67a01c8d7f.

docs/markdown/Generating-sources.md

@@ -111,16 +111,11 @@ and library dependency, especially if there are many generated headers:
 
 ```meson
 idep_foo = declare_dependency(
-    include_directories : libfoo.private_dir_include(),
+    sources : [foo_h, bar_h],
     link_with : [libfoo],
 )
 ```
 
-Adding the static library's private include directory to
-`include_directories` of `declare_dependency` will make sure all headers
-are generated before any sources of a target linking against libfoo are
-built.
-
 See [dependencies](Dependencies.md#declaring-your-own), and
 [reference](Reference-manual.md#decalre_dependency) for more information.