git-gui: git-diff knows submodules and textconv

git-gui's diff functions avoid using textconv filters on git < 1.6.1, or
asking about submodules on version before 1.7.2, but git-gui requires
git >= v2.36.  So, remove this now obsolete code.

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

Author: mark987

lib/diff.tcl

@@ -280,27 +280,22 @@ proc start_show_diff {cont_info {add_opts {}}} {
 	if {$w eq $ui_index} {
 		lappend cmd diff-index
 		lappend cmd --cached
-		if {[git-version >= "1.7.2"]} {
-			lappend cmd --ignore-submodules=dirty
-		}
+		lappend cmd --ignore-submodules=dirty
 	} elseif {$w eq $ui_workdir} {
 		if {[string first {U} $m] >= 0} {
 			lappend cmd diff
 		} else {
 			lappend cmd diff-files
 		}
 	}
-	if {![is_config_false gui.textconv] && [git-version >= 1.6.1]} {
+	if {![is_config_false gui.textconv]} {
 		lappend cmd --textconv
 	}
 
 	if {[string match {160000 *} [lindex $s 2]]
 	 || [string match {160000 *} [lindex $s 3]]} {
 		set is_submodule_diff 1
-
-		if {[git-version >= "1.6.6"]} {
-			lappend cmd --submodule
-		}
+		lappend cmd --submodule
 	}
 
 	lappend cmd -p
@@ -319,14 +314,6 @@ proc start_show_diff {cont_info {add_opts {}}} {
 		lappend cmd $path
 	}
 
-	if {$is_submodule_diff && [git-version < "1.6.6"]} {
-		if {$w eq $ui_index} {
-			set cmd [list submodule summary --cached -- $path]
-		} else {
-			set cmd [list submodule summary --files -- $path]
-		}
-	}
-
 	if {[catch {set fd [git_read_nice $cmd]} err]} {
 		set diff_active 0
 		unlock_index