[ntuple][skip-ci] fix some wrong Experimental leftovers in comments

(cherry picked from commit a2abd36)

Author: silverweed

tree/ntuple/inc/ROOT/RField/RFieldSequenceContainer.hxx

@@ -313,7 +313,7 @@ public:
 ////////////////////////////////////////////////////////////////////////////////
 
 /**
-\class ROOT::Experimental::RArrayAsRVecField
+\class ROOT::RArrayAsRVecField
 \brief A field for fixed-size arrays that are represented as RVecs in memory.
 \ingroup NTuple
 This class is used only for reading. In particular, it helps exposing

tree/ntuple/inc/ROOT/RNTupleDescriptor.hxx

@@ -235,7 +235,7 @@ class RClusterDescriptor final {
 public:
    // clang-format off
    /**
-   \class ROOT::Experimental::RClusterDescriptor::RColumnRange
+   \class ROOT::RClusterDescriptor::RColumnRange
    \ingroup NTuple
    \brief The window of element indexes of a particular column in a particular cluster
    */