Array Dimension Checker: Correct Groupsize Criterion

It is perfectly fine to have groups whose size (number of children)
is equal to the declared maximum (Item 4 of WELLDIMS).  It is only
questionable to have groups whose active size exceeds that of the
declared maximum.

Pointy Hat: @bska

src/opm/parser/eclipse/EclipseState/Schedule/ArrayDimChecker.cpp

@@ -114,7 +114,7 @@ namespace {
                 size = std::max(size, static_cast<std::size_t>(nwgmax));
             }
 
-            if (size >= static_cast<decltype(size)>(wdims.maxWellsPerGroup()))
+            if (size > static_cast<decltype(size)>(wdims.maxWellsPerGroup()))
             {
                 std::ostringstream os;
                 os << "Run uses maximum group size of " << size << ", but "