Update documentation for mysql_db notes (#50444)

* Simplify the requirement section to avoid duplicating info already in mysql_document_fragment.
* Package installation section simplified, mentioned RHEL; a typo fix in "than".
* added dnf for Fedora

lib/ansible/modules/database/mysql/mysql_db.py

@@ -67,8 +67,7 @@ requirements:
    - mysql (command line binary)
    - mysqldump (command line binary)
 notes:
-   - Requires the PyMySQL (Python 2.7 and Python 3.X) or MySQL-python (Python 2.X) package on the remote host,
-     as well as mysql and mysqldump binaries.
+   - Requires the mysql and mysqldump binaries on the remote host.
    - This module is B(not idempotent) when I(state) is C(import), and will import the dump file each time if run more than once.
 extends_documentation_fragment: mysql
 '''

lib/ansible/utils/module_docs_fragments/mysql.py

@@ -34,7 +34,7 @@ options:
     default: localhost
   login_port:
     description:
-      - Port of the MySQL server. Requires I(login_host) be defined as other then localhost if login_port is used.
+      - Port of the MySQL server. Requires I(login_host) be defined as other than localhost if login_port is used.
     default: 3306
   login_unix_socket:
     description:
@@ -66,9 +66,10 @@ requirements:
    - PyMySQL (Python 2.7 and Python 3.X), or
    - MySQLdb (Python 2.x)
 notes:
-   - Requires the PyMySQL (Python 2.7 and Python 3.X) or MySQL-python (Python 2.X) Python package on the remote host.
-     For Ubuntu, this is as easy as apt-get install python-pymysql. (See M(apt).) For CentOS/Fedora, this
-     is as easy as yum install python2-PyMySQL. (See M(yum).)
+   - Requires the PyMySQL (Python 2.7 and Python 3.X) or MySQL-python (Python 2.X) package on the remote host.
+     The Python package may be installed with apt-get install python-pymysql (Ubuntu; see M(apt)) or
+     yum install python2-PyMySQL (RHEL/CentOS/Fedora; see M(yum)). You can also use dnf install python2-PyMySQL
+     for newer versions of Fedora; see M(dnf).
    - Both C(login_password) and C(login_user) are required when you are
      passing credentials. If none are present, the module will attempt to read
      the credentials from C(~/.my.cnf), and finally fall back to using the MySQL