Some compiling warnings

When trying Valgrind I came across some compiling warnings with
USE_VALGRIND defined and --enable-cassert not configured.  This is
mainly because in this case we have MEMORY_CONTEXT_CHECKING defined
while USE_ASSERT_CHECKING not defined.

aset.c: In function ‘AllocSetFree’:
aset.c:1027:10: warning: unused variable ‘chunk_size’ [-Wunused-variable]
    Size  chunk_size = block->endptr - (char *) pointer;
          ^
generation.c: In function ‘GenerationFree’:
generation.c:633:8: warning: variable ‘chunksize’ set but not used [-Wunused-but-set-variable]
  Size  chunksize;
        ^

Attach a trivial patch for the fix.

Thanks
Richard