crucible: progress: drop the set() method

set() was broken and redundant.  Calling hold() and discarding the
returned object has the correct effect.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-roots.cc

@@ -1100,7 +1100,7 @@ BeesCrawl::hold_state(const BeesFileRange &bfr)
 void
 BeesCrawl::set_state(const BeesCrawlState &bcs)
 {
-	m_state.set(bcs);
+	m_state.hold(bcs);
 	m_ctx->roots()->crawl_state_set_dirty();
 }