git-gui: git rev-parse knows show_toplevel

git-gui has its own code to determine the worktree root for git-versions
earlier than 1.7.0, where git rev-parse learned this function.  git-gui
requires git v2.36 or later, so delete the now obsolete alternate code.

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

Author: mark987

git-gui.sh

@@ -1278,20 +1278,7 @@ if {![file isdirectory $_gitdir]} {
 load_config 0
 apply_config
 
-# v1.7.0 introduced --show-toplevel to return the canonical work-tree
-if {[package vcompare $_git_version 1.7.0] >= 0} {
-	set _gitworktree [git rev-parse --show-toplevel]
-} else {
-	# try to set work tree from environment, core.worktree or use
-	# cdup to obtain a relative path to the top of the worktree. If
-	# run from the top, the ./ prefix ensures normalize expands pwd.
-	if {[catch { set _gitworktree $env(GIT_WORK_TREE) }]} {
-		set _gitworktree [get_config core.worktree]
-		if {$_gitworktree eq ""} {
-			set _gitworktree [file normalize ./[git rev-parse --show-cdup]]
-		}
-	}
-}
+set _gitworktree [git rev-parse --show-toplevel]
 
 if {$_prefix ne {}} {
 	if {$_gitworktree eq {}} {