sandbox: drop man-db, now that /usr/share/man/* is purged

man-db is vestigial once the man page tree is removed in the cleanup
layer — the man binary has nothing to serve. Dropping it from the
install list recovers a few more MB and avoids shipping a no-op
package + its dependencies (groff-base, libpipeline1, etc).

Raised by greptile on the slim-image PR.

containers/Dockerfile

@@ -26,7 +26,7 @@ RUN apt-get update && \
     net-tools dnsutils whois \
     file xxd \
     jq parallel ripgrep grep \
-    less man-db procps htop \
+    less procps htop \
     iproute2 iputils-ping netcat-traditional \
     nmap ncat ndiff \
     sqlmap nuclei subfinder naabu ffuf \