This reverts commit 6a099257e8.
It is now clear that pinning the toolchain for cross compilation is not
necessary since we only use it for building to aarch64:
https://github.com/rust-lang/rust/issues/95926#issue-1199547707
"This problem doesn't currently show up when cross-compiling from x86_64
to aarch64, since aarch64 doesn't use static-pie by default, but
enabling PIE with -C relocation-model=pie triggers the same bug and
makes the resulting binaries segfault."
Fixes: #3962
Signed-off-by: Rob Bradford <robert.bradford@intel.com>