(PDB-5161) Drop json-contains; inline the code in the one caller

Remove json-contains in favor of just inlining the code since there's
only one caller, and it's perhaps a bit more immediately obvious
what's going on.  Explain the code's purpose a bit.

Author: rbrw

src/puppetlabs/puppetdb/query_eng/engine.clj

@@ -1528,10 +1528,15 @@
 
   JsonContainsExpression
   (-plan->sql [{:keys [field column-data array-in-path]} options]
-    (su/json-contains (if (instance? SqlRaw (:field column-data))
-                        (-> column-data :field :s)
-                        field)
-                      array-in-path))
+    (let [f (if (instance? SqlRaw (:field column-data))
+              (-> column-data :field :s)
+              field)]
+      ;; This distinction is necessary (at least) because @> cannot
+      ;; traverse into arrays, but should be otherwise preferred
+      ;; because it can use an index.
+      (if array-in-path
+        (hcore/raw (format "%s #> ? = ?" f))
+        (hcore/raw (format "%s @> ?" f)))))
 
   FnBinaryExpression
   (-plan->sql [{:keys [value function args operator]} options]

src/puppetlabs/puppetdb/scf/storage_utils.clj

@@ -244,12 +244,6 @@
   (hcore/raw
    (format "%s = ANY(?)" (first (hfmt/format column)))))
 
-(defn json-contains
-  [field array-in-path]
-  (if array-in-path
-    (hcore/raw (format "%s #> ? = ?" field))
-    (hcore/raw (format "%s @> ?" field))))
-
 (defn jsonb-path-binary-expression
   "Produce a predicate that compares against nested value with op and checks the
   existence of a (presumably) top-level value. The existence check is necessary