[GeometryType] Revert deprecation of GeometryType::BasicType for 2.6

As there are still some use cases that cannot be easily switched from using GeometryType::Basictype
to plain GeometryType, revert its deprecation for the 2.6 release.

This does **not** revert the deprecation of the GeometryType constructor from BasicType.

See merge request !88.

(cherry picked from commit 28afff5c)

CHANGELOG.md

@@ -20,8 +20,8 @@
   - There are new singletons and factory functions in the namespace `Dune::GeometryTypes`. These
     are now the official way to obtain a `GeometryType`.
 
-  - `GeometryType::BasicType` and the assorted constructor have been deprecated and will be removed
-    after the release of DUNE 2.6.
+  - The constructor taking a `GeometryType::BasicType` and a dimension has been deprecated and wil be
+    removed after the release of DUNE 2.6.
 
   - The assorted member functions `GeometryType::make...()` have been deprecated and will be removed
     after the release of DUNE 2.6.

dune/geometry/type.hh

@@ -277,12 +277,9 @@ namespace Dune
   {
   public:
 
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
     /** \brief Each entity can be tagged by one of these basic types
      *  plus its space dimension */
     enum
-    DUNE_DEPRECATED_MSG("BasicType is deprecated and will be removed after DUNE 2.6")
     BasicType {
       simplex,       //!< Simplicial element in any nonnegative dimension
       cube,          //!< Cube element in any nonnegative dimension
@@ -291,7 +288,6 @@ namespace Dune
       extended,      //!< Other, more general topology, representable as topologyId
       none           //!< Even more general topology, cannot be specified by a topologyId. Two GeometryTypes with 'none' type are equal if and only if they have the same dimension.
     };
-#pragma GCC diagnostic pop
 
   private: