Latin-1 source code was not being properly decoded when passed through
compile(). This was due to left-over special-casing before UTF-8 became the
default source encoding.

Closes issue #3574. Thanks to Victor Stinner for help with the patch.
diff --git a/Python/ast.c b/Python/ast.c
index 6d2fa09..60906a1 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -3160,9 +3160,6 @@
     if (encoding == NULL) {
         buf = (char *)s;
         u = NULL;
-    } else if (strcmp(encoding, "iso-8859-1") == 0) {
-        buf = (char *)s;
-        u = NULL;
     } else {
         /* check for integer overflow */
         if (len > PY_SIZE_MAX / 4)
@@ -3275,8 +3272,7 @@
         }
     }
     need_encoding = (!*bytesmode && c->c_encoding != NULL &&
-                     strcmp(c->c_encoding, "utf-8") != 0 &&
-                     strcmp(c->c_encoding, "iso-8859-1") != 0);
+                     strcmp(c->c_encoding, "utf-8") != 0);
     if (rawmode || strchr(s, '\\') == NULL) {
         if (need_encoding) {
             PyObject *v, *u = PyUnicode_DecodeUTF8(s, len, NULL);