Releasing doc: clean up duplicate sentence and outdated ninja dist`

0.52.0 is from 2019 and no longer relevant (even Debian stable is at
>1.0 by now), so no need to still document `ninja dist`. And it's
especially unhelpful since `ninja dist` doesn't support all the options
discussed on this page for `meson dist`.

Author: rgommers

docs/markdown/Creating-releases.md

@@ -8,21 +8,12 @@ In addition to development, almost all projects provide periodical
 source releases. These are standalone packages (usually either in
 tar or zip format) of the source code. They do not contain any
 revision control metadata, only the source code.  Meson provides
-a simple way of generating these, with the `meson dist` command.
-
-Meson provides a simple way of generating these. It consists of a
-single command *(available since 0.52.0)*:
+a simple way of generating these, with the `meson dist` command:
 
 ```sh
 meson dist
 ```
 
-or alternatively (on older Meson versions with `ninja` backend):
-
-```sh
-ninja dist
-```
-
 This creates a file called `projectname-version.tar.xz` in the build
 tree subdirectory `meson-dist`. This archive contains the full
 contents of the latest commit in revision control including all the