treewide: replace shell_commands module in documentation

Signed-off-by: Dylan Laduranty <dylan.laduranty@mesotic.com>

examples/default/README.md

@@ -4,12 +4,12 @@ This application is a showcase for RIOT's hardware support. Using it
 for your board, you should be able to interactively use any hardware
 that is supported.
 
-To do this, the application uses the `shell` and `shell_commands`
+To do this, the application uses the `shell` and `shell_cmds_default`
 modules and all the driver modules each board supports.
 
 `shell` is a very simple interactive command interpreter that can be
 used to call functions.  Many of RIOT's modules define some generic
-shell commands. These are included via the `shell_commands` module.
+shell commands. These are included via the `shell_cmds_default` module.
 
 Additionally, the `ps` module which provides the `ps` shell command is
 included.

sys/shell/cmds/nice.c

@@ -13,7 +13,8 @@
  * @file
  * @brief       A shell command to change the niceness (inverse priority) of a thread
  *
- * @note        Enable this by using the modules shell_commands and nice
+ * @note        Enable this by using the modules shell_cmds_default and
+ *              shell_cmd_nice
  *
  * @author      Marian Buschsieweke <marian.buschsieweke@ovgu.de>
  *

sys/shell/doc.txt

@@ -15,11 +15,11 @@ Shell Commands
 
 Certain modules such as `ps`, `saul_reg`, or `gnrc_icmpv6_echo` can expose
 (some of) their functionality not only as C-API, but also as shell command.
-Using the module `shell_commands` will enable the shell integration of the used
+Using the module `shell_cmds_default` will enable the shell integration of the used
 modules, if it exists.
 
 A few rarely needed shell commands that needs to be used in addition to the
-`shell_commands` and the module providing the C-API. Examples include
+`shell_cmds_default` and the module providing the C-API. Examples include
 `shell_cmd_nice`, `shell_cmd_gnrc_udp`, or `shell_random_cmd`.
 Consult the documentation of the modules to find out whether they have a
 shell integration and how to enable it.

tests/sys/shell/ReadMe.txt

@@ -1,7 +1,7 @@
 This application shows how to use own or the system shell commands. In order to use
 the system shell commands:
 
-1. Additionally to the module: shell, shell_commands,
+1. Additionally to the module: shell, shell_cmds_default,
    the module for the corresponding system command is to include, e.g.
    module ps for the ps command (cf. the Makefile in the application root
    directory).