fix(remove-system.map): skip read-only files instead of aborting

[maybebyte]

Summary

remove-system.map shreds System.map* files because they expose a kernel
symbol-to-address map useful for exploitation. The deletion loop aborts on
the first read-only match, so writable copies in other locations are left on
disk while the run still reports success.

Changes

• Root cause: the read-only branch of the loop calls exit 0, which
  terminates the whole script on the first non-writable System.map (commonly
  /boot, which is often read-only). Later writable copies under /usr/src,
  /lib/modules, and / are then never shredded, and the Done. Success.
  summary is skipped even though the exit code reports success.
• Replace exit 0 with continue so each read-only file is noted and the
  loop proceeds through the remaining locations. The exit code is unchanged.

Testing

• Minimal reproduction of the loop's control flow: with exit 0 the run stops
  after the first read-only entry (no summary printed); with continue it
  processes the following writable entry and prints Done. Success.
• shellcheck on the modified script: no new findings (only a pre-existing
  SC1091 info note on the unrelated source line).
• No automated tests cover this script.

Notes for reviewers

• Behavior delta: on systems where an early System.map (e.g. under /boot)
  is read-only, writable copies elsewhere that were previously skipped will now
  be shredded — the tool's intended behavior.