Enhance tests

* Now that JSON_SORT_KEYS is implemented, take it into use with the
  valid and valid-strip suites. This is to ensure that the tests
  remain valid even if the string hash function is changed in the
  future.

* Remove test_dump API test. Instead, implement the same tests more
  elegantly in the encoding-flags suite.

test/suites/encoding-flags/indent-compact-array/env

@@ -0,0 +1,2 @@
+export JSON_INDENT=4
+export JSON_COMPACT=1

test/suites/encoding-flags/indent-compact-array/input

@@ -0,0 +1 @@
+[1, 2]

test/suites/encoding-flags/indent-compact-array/output

@@ -0,0 +1,4 @@
+[
+    1,
+    2
+]