Separation of TrixiShallowWater.jl (#1809)

* remove wet_dry functionality for SWE-1D

* remove wet_dry functionality for SWE-2D

* remove twolayer equations

* remove limiters from swe_quasi_1d

* remove export of min_max_speed_chen_noelle

* remove elixirs

* update news.md

* add unit tests to increase coverage

* Change news.md according to code review

Co-authored-by: Hendrik Ranocha <[email protected]>

---------

Co-authored-by: Andrew Winters <[email protected]>
Co-authored-by: Hendrik Ranocha <[email protected]>

NEWS.md

@@ -4,6 +4,19 @@ Trixi.jl follows the interpretation of [semantic versioning (semver)](https://ju
 used in the Julia ecosystem. Notable changes will be documented in this file
 for human readability.
 
+## Changes when updating to v0.7 from v0.6.x
+
+#### Added
+
+#### Changed
+
+#### Deprecated
+
+#### Removed
+- Some specialized shallow water specific features are no longer available directly in
+  Trixi.jl, but are moved to a dedicated repository: [TrixiShallowWater.jl](https://github.com/trixi-framework/TrixiShallowWater.jl). This includes all features related to wetting and drying, as well as the `ShallowWaterTwoLayerEquations1D` and `ShallowWaterTwoLayerEquations2D`.
+  However, the basic shallow water equations are still part of Trixi.jl. We'll also be updating the TrixiShallowWater.jl documentation with instructions on how to use these relocated features in the future.
+
 ## Changes in the v0.6 lifecycle
 
 #### Added