Remove assertion about theoretical path separators (elastic#122069)

The only real path separators are either forward or back slash. Trying
to use something else like newline fails to even parse as a path on
windows. This commit removes testing of other separators.

closes elastic#121872

Author: rjernst

libs/entitlement/src/test/java/org/elasticsearch/entitlement/runtime/policy/FileAccessTreeTests.java

@@ -102,9 +102,6 @@ public void testForwardSlashes() {
         // Forward slashes also work
         assertThat(tree.canRead(path("a/b")), is(true));
         assertThat(tree.canRead(path("m/n")), is(true));
-
-        // In case the native separator is a backslash, don't treat that as an escape
-        assertThat(tree.canRead(path("m\n")), is(false));
     }
 
     FilesEntitlement entitlement(String... values) {