[ELF] Drop Android specific workaround -m aarch64_elf64_le_vec

`extern const bfd_target aarch64_elf64_le_vec;` is a variable in BFD.
It was somehow misused as an emulation by Android.

```
% aarch64-linux-gnu-ld -m aarch64_elf64_le_vec a.o
aarch64-linux-gnu-ld: unrecognised emulation mode: aarch64_elf64_le_vec
Supported emulations: aarch64linux aarch64elf aarch64elf32 aarch64elf32b aarch64elfb armelf armelfb aarch64linuxb aarch64linux32 aarch64linux32b armelfb_linux_eabi armelf_linux_eabi
```

Acked by Stephen Hines, who removed the flag from Android a while back.