buf0lru.c: Always #include "srv0srv.h"

buf_block_get_lock_mutex(), buf_frame_get_lock_mutex(): Remove.

mtr0log.ic: Remove #include "page0page.h" and replace the page_
functions with lower-level ones to break an #include cycle.

dict0dict.ic: Remove unnecessary #include "trx0undo.h" and "trx0sys.h"
that would create an #include cycle.