glocalfile: Never require G_LOCAL_FILE_STAT_FIELD_ATIME

Some filesystems don't have meaningful access times under at least some circumstances (see #2189 (closed), #2205 (closed)). In this situation the traditional stat() and related kernel interfaces have to put something meaningless in the st_atime field, and have no way to signal that it is meaningless.

However, statx() does have a way to signal that the atime is meaningless: if the filesystem doesn't provide a useful access time, it will unset the STATX_ATIME bit (as well as filling in the same meaningless value for the stx_atime field that stat() would have used, for compatibility). We don't actually need the atime, so never include it in the required mask. This was already done for one code path in commit 6fc143bb "gio: Allow no atime from statx" to fix #2189 (closed), but other callers were left unchanged in that commit, and receive the same change here.

It is not actually guaranteed that any of the flags in the returned stx_mask will be set (the only guarantee is that items in STATX_BASIC_STATS have at least a harmless compatibility value, even if their corresponding flag is cleared), so it might be better to follow this up by removing the concept of the required mask entirely. However, as of Linux 5.8 it looks as though STATX_ATIME is the only flag in STATX_BASIC_STATS that might be cleared in practice, so this simpler change fixes the immediate regression.

Resolves: #2205 (closed)