build: make warning about rebuilt pkgs a -v msg (MR 2047)

Let warnings like the following not get displayed in the regular
pmbootstrap output anymore, only in 'pmbootstrap log' if -v / --verbose
was used. This message informs the user that a package's dependencies
are newer than the package itself. But the WARNING makes it sound like
this is something to be concerned about, whereas in reality this is
fine. In this example, postmarketos-mkinitfs has gotten a new feature /
fix after postmarketos-base and there's no need to rebuild
postmarketos-base.

  [18:02:59] WARNING: postmarketos-base depends on rebuilt package(s)
  postmarketos-mkinitfs (use 'pmbootstrap build postmarketos-base --force'
  if necessary!)

[skip ci] already built in CI, change is trivial

pmb/build/_package.py

@@ -171,11 +171,8 @@ def is_necessary_warn_depends(args, apkbuild, arch, force, depends_built):
         ret = True
 
     if not ret and len(depends_built):
-        # Warn of potentially outdated package
-        logging.warning("WARNING: " + pkgname + " depends on rebuilt" +
-                        " package(s) " + ",".join(depends_built) + " (use" +
-                        " 'pmbootstrap build " + pkgname + " --force' if" +
-                        " necessary!)")
+        logging.verbose(f"{pkgname}: depends on rebuilt package(s): "
+                        f" {', '.join(depends_built)}")
 
     logging.verbose(pkgname + ": build necessary: " + str(ret))
     return ret