STYLE: Remove redundant checks in ProcessObject::VerifyPreconditions()

Removed redundant checks of required named inputs, which were performed already
in the previous lines of code.

Partially reverts commit bf6f106
"BUG: VerifyPreconditions checks required named inputs", April 23, 2013.

Author: N-Dekker

Modules/Core/Common/src/itkProcessObject.cxx

@@ -1340,20 +1340,6 @@ ProcessObject::VerifyPreconditions() ITKv5_CONST
     }
   }
 
-  /**
-   * Verify the require named inputs.
-   */
-  auto i = m_RequiredInputNames.begin();
-  while (i != m_RequiredInputNames.end())
-  {
-    if (this->GetInput(*i) == nullptr)
-    {
-      itkExceptionMacro("Required Input " << *i << "is not specified!"
-                                          << " The required inputs are expected to be the first inputs.");
-    }
-    ++i;
-  }
-
   /**
    * Count the number of required indexed inputs which have been assigned
    */