mm, fs: remove remaining PAGE_CACHE_* and page_cache_{get,release} usage

Mostly direct substitution with occasional adjustment or removing
outdated comments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/btrfs/tests/extent-io-tests.c b/fs/btrfs/tests/extent-io-tests.c
index ac3a06d..70948b1 100644
--- a/fs/btrfs/tests/extent-io-tests.c
+++ b/fs/btrfs/tests/extent-io-tests.c
@@ -239,7 +239,7 @@
 	end = 0;
 	/*
 	 * Currently if we fail to find dirty pages in the delalloc range we
-	 * will adjust max_bytes down to PAGE_CACHE_SIZE and then re-search.  If
+	 * will adjust max_bytes down to PAGE_SIZE and then re-search.  If
 	 * this changes at any point in the future we will need to fix this
 	 * tests expected behavior.
 	 */