[kcm] Escape connection name in close dialog

Summary:
Due to MessageDialog being used we cannot change the text format on the
label, therefore we have to escape the connection name.

This expression is copied from plasma-framework internals.

Test Plan:
Set my ssid to foo<b>123</b>
Tried to remove the SSID
No bold text anymore

Reviewers: Plasma, jgrulich

Reviewed By: jgrulich

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D27545