Revert "Reland "[AArch64] Fix data race on RegisterBank initialization.""

This reverts commit 8e1ca948.

New failing at
 http://lab.llvm.org:8011/builders/clang-armv7-linux-build-cache/builds/25929

I did reproduce and pass the previous failure at
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-autoconf/builds/46803/steps/annotate/logs/stdio