[asan] Remove special case mapping on Android/AArch64.

[asan] Remove special case mapping on Android/AArch64.

ASan shadow on Android starts at address 0 for both historic and
performance reasons. This is possible because the platform mandates
-pie, which makes lower memory region always available.

This is not such a good idea on 64-bit platforms because of MAP_32BIT
incompatibility.

This patch changes Android/AArch64 mapping to be the same as that of
Linux/AAarch64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243548 91177308-0d34-0410-b5e6-96231b3b80d8