Remove comment about multi VFD duplication (#5029)

Author: derobins

src/H5warnings.h

@@ -18,10 +18,6 @@
 #define H5warnings_H
 
 /* Macros for enabling/disabling particular GCC / clang warnings
- *
- * These are duplicated in H5FDmulti.c (we don't want to put them in the
- * public header and the multi VFD can't use private headers). If you make
- * changes here, be sure to update those as well.
  *
  * (see the following web-sites for more info:
  *      http://www.dbp-consulting.com/tutorials/SuppressingGCCWarnings.html