reloc: stop removing entire BUILDDIR

We found that user can mistakenly break system with --builddir option,
something like './reloc/build_deb.sh --builddir /'.
To avoid that we need to stop removing entire $BUILDDIR, remove
directories only we have to clean up before building deb package.

See: scylladb/scylla-python3#23 (comment)

Closes scylladb#9351

reloc/build_deb.sh

@@ -38,7 +38,7 @@ if [ ! -e $RELOC_PKG ]; then
     exit 1
 fi
 RELOC_PKG=$(readlink -f $RELOC_PKG)
-rm -rf $BUILDDIR
+rm -rf "$BUILDDIR"/scylla-package "$BUILDDIR"/scylla-package.orig "$BUILDDIR"/debian
 mkdir -p $BUILDDIR/scylla-package
 tar -C $BUILDDIR/scylla-package -xpf $RELOC_PKG
 cd $BUILDDIR/scylla-package