Do not use Soup.Status.get_phrase

[spaetz]

Hi, Debian fails to build from source
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=993088

../../src/Services/Network.vala:69.19-69.40: error: The name `get_phrase' does not exist in the context of `Soup.Status' (libsoup-2.4)
	    var reason = Soup.Status.get_phrase (code);
	                 ^^^^^^^^^^^^^^^^^^^^^^

I don't know why that code is not available, according to the API docs it should be. However, the docs describe the API as
**"There is no reason for you to ever use this function."** (https://valadoc.org/libsoup-2.4/Soup.Status.get_phrase.html).

Instead "you should just look at the message's reason_phrase". Given that the function network.describe_error() is only used twice, it should be easy to replace it:

1. tootle/src/Services/Cache/ImageCache.vala

   Line 10 in cb7a179

   var error = network.describe_error (code);

   
   instead of network.describe_error (code), we can use the msg that is available in that function. and

2. tootle/src/Services/Network/Network.vala

   Line 59 in ddba63d

   ecb ((int32) status, describe_error ((int32) status));

same, we also have the message available in that function and can use the "reason_phrase". This brings tootle in line with the recommended API as per the libsoup authors.

[spaetz]

Just discovered this is aduplicate of #322 and has been filed as #320