Remove gconf2 dependency (#3244)

This is an attempt to fix the issue reported by users who cannot install
Simplenote on various Linux systems because the `gconf2` dependency
cannot be satisfied. See
#3241

The [`electron-builder` docs](https://www.electron.build/configuration/linux.html)
mention that `gconf2` can give issues if one wants to support
[KDE](https://kde.org/).

> If need to support KDE, `gconf2` and `gconf-service` should be removed
> as it’s no longer used
> [by GNOME](https://packages.debian.org/bullseye/gconf2).

Moreover,
[the `gconf2` entry in the Debian packages repository](https://packages.debian.org/bullseye/gconf2)
states:

> This package is for legacy applications and no longer used by GNOME.

Given the above, this PR is an attempt to see what the app would do
without the dependency. My guess is that everything should run fine in
most modern systems, because all information points to `gconf2` not
being in use there.

electron-builder.json

@@ -110,8 +110,7 @@
     }
   ],
   "deb": {
-    "compression": "gz",
-    "depends": ["gconf2"]
+    "compression": "gz"
   },
   "afterSign": "./after_sign_hook.js",
   "afterAllArtifactBuild": "./after_sign_hook.js"