Update obsolete header files:

* remove obsolete m-mutex header file
* mark m-concurrent, m-shared and m-i-shared as obsolete (They won't support new memory model)

m-shared.h

@@ -29,6 +29,10 @@
 #include "m-atomic.h"
 #include "m-genint.h"
 
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ > 201710L
+#warning The header m-shared.h is obsolete. Use m-shared-ptr header instead.
+#endif
+
 M_BEGIN_PROTECTED_CODE
 
 /* Define shared pointer and its function.