Remove TODO file

Was outdated. Nowadays https://gitlab.xfce.org is used to track issues

TODO

-Important for Thunar 1.2
-========================
-
- - The layouting code for ThunarLocationButtons is still buggy. Problem shows
-   with paths that include a very long directory; you cannot scroll to the
-   last path component then.
-
- - A design for the ThunarDesktopView module must be developed and later
-   be implemented.
-
- - We need a suite of unit tests and probably high-level tests, that enable
-   us to test parts of the file manager automatically and isolate bugs
-   early.
-
- - Setup gtk-doc to present developers with the internal API of Thunar
-   to ease development of core modules (and later plugins).
-
- - Write good user documentation. Must be both precise and complete.
-
- - We need some easy way to manage diagrams and related developer
-   information, which also includes results from discussions on
-   thunar-dev.
-
- - The HACKING file must be updated with strict rules about how
-   development of Thunar core modules is to be done, and what
-   material each developer in addition to the source code.
-