patch 8.1.1048: minor issues with tests

Problem:    Minor issues with tests.
Solution:   Delete unused test OK file.  Add missing entries in list of tests.
            Fix readme file. (Masato Nishihata, closes #4160)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 8581700..81d0dc7 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -224,6 +224,7 @@
 	test_searchpos \
 	test_set \
 	test_sha256 \
+	test_shortpathname \
 	test_signals \
 	test_signs \
 	test_smartindent \
@@ -258,6 +259,7 @@
 	test_true_false \
 	test_undo \
 	test_unlet \
+	test_user_func \
 	test_usercommands \
 	test_utf8 \
 	test_utf8_comparisons \