sstables: Rename filename($component) calls to ${component}_filename()

There's a generic sstable::filename(component_type) method that returns
a file name for the given component. For "popular" components, namely
TOC, Data and Index there are dedicated sstable methods to get their
names. Fix existing callers of the generic method to use the former.
It's shorter, nicer and makes further patching simpler.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

test/lib/sstable_utils.hh

@@ -155,7 +155,7 @@ public:
     void rewrite_toc_without_component(component_type component) {
         SCYLLA_ASSERT(component != component_type::TOC);
         _sst->_recognized_components.erase(component);
-        remove_file(_sst->filename(component_type::TOC)).get();
+        remove_file(_sst->toc_filename()).get();
         _sst->_storage->open(*_sst);
         _sst->seal_sstable(false).get();
     }