jbd2: drop pointless shrinker batch initialization

In jbd2_journal_init_common() we set batch size of a shrinker shrinking
checkpointed buffers to journal->j_max_transaction_buffers. But that is
guaranteed to be 0 at that point so we effectively stay with the default
shrinker batch size of 128. It has been like this since introduction of
jbd2 shrinkers so just drop the pointless initialization.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20240624170127.3253-4-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>