build: revert -Wvla from #15342

build: revert -Wvla from #15342

 - VLAs are in GCC and Clang, and are there to stay forever,
   if only to be compatible with all the software that is already
   out there.
   - Theoretical debates about VLA being hard to implement are
     long superceded by th actual implentations
 - Before setting this flag is would be required to first start
   work on fixing all the fallout/warnings that will arise from
   setting -Wvla
 - Allocating large variable/stuctures on the stack could be asking
   for trouble, but changes that ceph tools are going to be running
   on small embedded devices are rather slim.

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>