doc: Drop the SPHINX progress message

This message is not needed since sphinx is now running in quiet mode.

Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

doc/Makefile

@@ -51,7 +51,7 @@ loop_cmd = $(echo-cmd) $(cmd_$(1)) || exit;
 # $5 reST source folder relative to $(srctree)/$(src),
 #    e.g. "media" for the linux-tv book-set at ./doc/media
 
-quiet_cmd_sphinx = SPHINX  $@ --> file://$(abspath $(BUILDDIR)/$3/$4)
+quiet_cmd_sphinx =
       cmd_sphinx = $(MAKE) -s BUILDDIR=$(abspath $(BUILDDIR)) $(build)=doc/media $2 && \
 	PYTHONDONTWRITEBYTECODE=1 \
 	BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \