libgettextpo: Remove static variable pass_comments.

libgettextpo: Remove static variable pass_comments.

* gettext-tools/src/read-catalog-abstract.h (ABSTRACT_CATALOG_READER_TY): Add
pass_comments field.
* gettext-tools/src/read-catalog-abstract.c (catalog_reader_alloc): Initialize
pass_comments field.
* gettext-tools/src/read-catalog.c (default_parse_brief): Assign the
pass_comments field, instead of calling po_lex_pass_comments.
* gettext-tools/src/po-lex.h (po_lex_pass_comments): Remove declaration.
* gettext-tools/src/po-lex.c (pass_comments): Remove variable.
(po_gram_lex): Update.
(po_lex_pass_comments): Remove function.