binman: Drop CheckEntries()

This method introduces a separation between packing and checking that is
different for sections. In order to handle compression properly, we need
to be able to deal with a section's size being smaller than the
uncompressed size of its contents. It is easier to make this work if
everything happens in the Pack() method.

The only real user of CheckEntries() is entry_Section and it can call it
directly. Drop the call from 'control' and handle it locally.

Signed-off-by: Simon Glass <sjg@chromium.org>