Revert "Add a static_assert confirming that DiagnosticBuilder is small"

This reverts commit a32feed0db.

This assert doesn't hold in 32-bit builds, I didn't do the math right.

clang/lib/Basic/Diagnostic.cpp

@@ -40,9 +40,6 @@
 
 using namespace clang;
 
-static_assert(sizeof(DiagnosticBuilder) <= 2 * sizeof(void *),
-              "DiagnosticBuilder should be small, see class doc comments");
-
 const DiagnosticBuilder &clang::operator<<(const DiagnosticBuilder &DB,
                                            DiagNullabilityKind nullability) {
   StringRef string;