Remove declaration of constexpr member kDynamicSize in MemRefType

[mehdi_amini]

Summary

This member is already publicly declared on the base class. The
redundant declaration is mangled differently though and in some
unoptimized build it requires a definition to also exist. However we
have a definition for the base ShapedType class, removing the
declaration here will redirect every use to the base class member
instead.

mlir/include/mlir/IR/StandardTypes.h

public:
   ArrayRef<AffineMap> getAffineMaps() const;
 
   /// Returns the memory space in which data referred to by this memref resides.
   unsigned getMemorySpace() const;
 
   // TODO: merge these two special values in a single one used everywhere.
   // Unfortunately, uses of `-1` have crept deep into the codebase now and are
   // hard to track.
-  static constexpr int64_t kDynamicSize = -1;
   static int64_t getDynamicStrideOrOffset() {
     return ShapedType::kDynamicStrideOrOffset;
   }
 
   static bool kindof(unsigned kind) { return kind == StandardTypes::MemRef; }
 
 private:
   /// Get or create a new MemRefType defined by the arguments.  If the resulting