git-gui: git-diff-index always knows submodules

git-gui asks for submodule info only on git-versions >=1.72, which
introduced such capability. But, git-gui requires git version >= 2.36,
so this alternate code path is obsolete. Remove it.

Signed-off-by: Mark Levedahl <[email protected]>

Author: mark987

git-gui.sh

@@ -1544,11 +1544,7 @@ proc rescan_stage2 {fd after} {
 
 	set rescan_active 2
 	ui_status [mc "Scanning for modified files ..."]
-	if {[git-version >= "1.7.2"]} {
-		set fd_di [git_read [list diff-index --cached --ignore-submodules=dirty -z [PARENT]]]
-	} else {
-		set fd_di [git_read [list diff-index --cached -z [PARENT]]]
-	}
+	set fd_di [git_read [list diff-index --cached --ignore-submodules=dirty -z [PARENT]]]
 	set fd_df [git_read [list diff-files -z]]
 
 	fconfigure $fd_di -blocking 0 -translation binary -encoding binary