Fix phone is not in {, non}silence.txt

[aevernon]

The latest version of sw-ms98-dict.text from http://www.openslr.org/resources/5/switchboard_word_alignments.tar.gz contains the following header on line 1:

file: $SWB/data/dictionary/sw-ms98-dict.text

This ends up in lexicon0.txt, which causes utils/validate_dict_dir.pl to
fail with the following error:

--> ERROR: phone "$swb/data/dictionary/sw-ms98-dict.text" is not in {, non}silence.txt (line 10399)

This in turn causes utils/prepare_lang.sh to fail.

Update dict.patch so that it removes the file header from sw-ms98-dict.text.

[danpovey]

That line has always been there; I think the regression was caused by some fixes to awk scripts that we made for mawk compatibility. But your fix works, so merging.