utils: Drop unused BwrapCmd

The only consumer of BwrapCmd (install_via_bootupd in
bootloader.rs) switched to ChrootCmd in the previous commit, so
BwrapCmd and the bubblewrap-based execution path have no remaining
callers in the workspace.

Assisted-by: Claude Code (Opus 4.7 1M)
Signed-off-by: cdellacqua <carlo.dellacqua97@gmail.com>

Author: cdellacqua

crates/utils/src/bwrap.rs

@@ -2,8 +2,6 @@
 //! things here that only depend on the standard library and
 //! "core" crates.
 //!
-mod bwrap;
-pub use bwrap::*;
 mod chroot;
 pub use chroot::*;
 mod command;