perf(git): fold revspec validation into the cat-file -p the loader needs anyway

lua/git/repo.lua

@@ -343,18 +343,4 @@ function M.rev_parse(worktree, ref, short)
     return trimmed ~= "" and trimmed or nil
 end
 
----Verify a revspec resolves to an existing git object. `cat-file -e` is
----git's cheapest existence check, and unlike `rev-parse --verify` it
----also accepts the `<commit>:<path>` form that BufReadCmd revspec URIs
----use.
----@param worktree string
----@param revspec string
----@return boolean
-function M.object_exists(worktree, revspec)
-    return util.exec(
-        { "git", "cat-file", "-e", revspec },
-        { cwd = worktree, silent = true }
-    ) ~= nil
-end
-
 return M