Revert "[sanitizer] Allow the sanitizer allocator to use a non-fixed address...

Revert "[sanitizer] Allow the sanitizer allocator to use a non-fixed address range. An allocator with a non-fixed address range will be attack-resistan. NFC for the sanitizers at this point."

This reverts commit r267094, because it broke a lot of MSAN tests in AArch64.
Being NFC and all, this needs some deeper investigation before it goes in again.

llvm-svn: 267136