jbd2: cleanup unused functions declarations from jbd2.h

During code review found no references of few of these below function
declarations. This patch cleans those up from jbd2.h

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/30d1fc327becda197a4136cf9cdc73d9baa3b7b9.1642416995.git.riteshh@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>