Make page titles succinct

The docusaurus site shows breadcrumbs, so the prefixes are unnecessary

Author: kenstir

docs/pn-setup-guide/configure-hemlock-app.md

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-# Push Notifications: Configure the Hemlock app
+# Configure the Hemlock app
 
 This guide is for the mobile app developer.
 

docs/pn-setup-guide/create-an-action-trigger.md

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-# Push Notifications: Create an action trigger
+# Create an action trigger
 
 This guide is for the Evergreen Administrator.
 It will help you set up your Evergreen (EG) server for sending a push notifications with an action trigger.  It assumes that your System Administrator has already installed the `hemlock-sendmsg` daemon, and it's listening on `localhost:8842`.

docs/pn-setup-guide/install-sendmsg-daemon.md

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-# Push Notifications: Install the hemlock-sendmsg daemon
+# Install the hemlock-sendmsg daemon
 
 This guide is for the Evergreen System Administrator.
 

docs/pn-setup-guide/setup-firebase-project.md

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-# Push Notifications: Set up the Firebase project
+# Set up the Firebase project
 
 This guide is for the administrator of the Firebase project associated with your app.  If I released your app, you already have a Firebase project.  Contact me for an invitation.