Remove redundant MADV_POPULATE_READ from MappedDiskVector

Summary:
MADV_POPULATE_WRITE subsumes MADV_POPULATE_READ: a write fault reads the
page from disk before marking it dirty, so it catches the same I/O errors
(corruption, missing extents) that POPULATE_READ detects. Since the
constructor already calls populateForWrite over the full mapping region,
the earlier POPULATE_READ call is redundant.

This also removes the now-unused `shouldPopulate` / `populate` parameter
from `open()` and the private constructor—it existed solely to control
the POPULATE_READ call.

Reviewed By: genevievehelsel

Differential Revision: D99742007

fbshipit-source-id: f6d4f54df60ba4ab0bdc701b150dc0da00de2203

Author: MichaelCuevas

eden/fs/inodes/InodeTable.h

@@ -99,7 +99,7 @@ class InodeTable {
       EdenStatsPtr stats) {
     return std::unique_ptr<InodeTable>{new InodeTable{
         MappedDiskVector<Entry>::template open<
-            detail::InodeTableEntry<OldRecords>...>(path, true),
+            detail::InodeTableEntry<OldRecords>...>(path),
         std::move(stats)}};
   }