ctf: Remove redundant declarations of lexer/parser functions

ctf: Remove redundant declarations of lexer/parser functions

I get these warnings:

      CC       libctf_parser_la-lexer.lo
    lexer.c:857:17: error: redundant redeclaration of ‘yyunput’ [-Werror=redundant-decls]
      857 |
          |                 ^
    /home/simark/src/babeltrace/src/plugins/ctf/common/metadata/lexer.l:55:13: note: previous declaration of ‘yyunput’ was here
       55 | static void yyunput (int c, register char * yy_bp , yyscan_t yyscanner)
          |             ^~~~~~~

      CC       libctf_parser_la-lexer.lo
    lexer.c:871:12: error: redundant redeclaration of ‘input’ [-Werror=redundant-decls]
      871 | #else
          |            ^
    /home/simark/src/babeltrace/src/plugins/ctf/common/metadata/lexer.l:55:12: note: previous declaration of ‘input’ was here
       55 | static int input (yyscan_t yyscanner) __attribute__((unused));
          |            ^~~~~

      CC       libctf_parser_la-parser.lo
    /home/simark/src/babeltrace/src/plugins/ctf/common/metadata/parser.y:63:5: error: redundant redeclaration of ‘yyparse’ [-Werror=redundant-decls]
       63 | int yyparse(struct ctf_scanner *scanner, yyscan_t yyscanner);
          |     ^~~~~~~
    In file included from /home/simark/src/babeltrace/src/plugins/ctf/common/metadata/parser-wrap.h:41,
                     from /home/simark/src/babeltrace/src/plugins/ctf/common/metadata/parser.y:47:
    parser.h:192:5: note: previous declaration of ‘yyparse’ was here
      192 | int yyparse (struct ctf_scanner *scanner, yyscan_t yyscanner);
          |     ^~~~~~~

Because of the __attribute__((unused)), when removing the declarations
of yyunput and input from lexer.l, I expected to get a
"-Wunused-function" warning.  But that doesn't seem to be the case (even
when manually enabling -Wunused-function), so I'm giving a shot at
removing those declarations, since they may not be essential.

The yyparse declaration is not essential, since there's one already in
the generated parser.h.

There is a slight possibility that older bison versions (I'm using
3.4.2) produce different results, but I can't easily test right now.

Change-Id: I73ff02896db1f40d476757b3207629a3ff20ac39
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2274
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>