chore: stop treating dirs as having size 128 (#10750)

Resp. directories for the database, and both dirs and symlinks for
`FileInfo.FileSize`. Instead handle it in the UI progress percentage. We
even already have special cases there for deletions, might as well
handle directories just like any other zero-sized needed item there.

This went through the very thorough testing of running it on my laptop,
the migration was applied and it seemed to be working fine after.

---------

Signed-off-by: Simon Frei <freisim93@gmail.com>

lib/protocol/bep_fileinfo.go

@@ -389,16 +389,6 @@ func (f FileInfo) HasPermissionBits() bool {
 	return !f.NoPermissions
 }
 
-func (f FileInfo) FileSize() int64 {
-	if f.Deleted {
-		return 0
-	}
-	if f.IsDirectory() || f.IsSymlink() {
-		return SyntheticDirectorySize
-	}
-	return f.Size
-}
-
 func (f FileInfo) BlockSize() int {
 	if f.RawBlockSize < MinBlockSize {
 		return MinBlockSize