Remove redundant code (#9373)

## Problem

There is double update of resize cache in `put_rel_truncation`
Also `page_server_request` contains check that fork is MAIN_FORKNUM
which
1. is incorrect (because Vm/FSM pages are shreded in the same way as
MAIN fork pages and
2. is redundant because `page_server_request` is never called for `get
page` request so first part to OR condition is always true.

## Summary of changes

Remove redundant code

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>

pageserver/src/pgdatadir_mapping.rs

@@ -1545,9 +1545,6 @@ impl<'a> DatadirModification<'a> {
             // Update relation size cache
             self.tline.set_cached_rel_size(rel, self.lsn, nblocks);
 
-            // Update relation size cache
-            self.tline.set_cached_rel_size(rel, self.lsn, nblocks);
-
             // Update logical database size.
             self.pending_nblocks -= old_size as i64 - nblocks as i64;
         }

pgxn/neon/pagestore_smgr.c

@@ -1092,8 +1092,7 @@ page_server_request(void const *req)
 	 * Current sharding model assumes that all metadata is present only at shard 0.
 	 * We still need to call get_shard_no() to check if shard map is up-to-date.
 	 */
-	if (((NeonRequest *) req)->tag != T_NeonGetPageRequest ||
-		((NeonGetPageRequest *) req)->forknum != MAIN_FORKNUM)
+	if (((NeonRequest *) req)->tag != T_NeonGetPageRequest)
 	{
 		shard_no = 0;
 	}