Drop redundant HasText costrants from ExtractNgrams

The `ExtractNgrams` typeclass _definition_ imposed a redundant
`HasText` constraint, forcing all the _instances_ to have `HasText`
defined even though the instance didn't make any use of that.

That is overly-rigid, and it has been fixed by this commit.

src/Gargantext/Core/Text/Terms.hs

@@ -116,7 +116,7 @@ data ExtractedNgrams = SimpleNgrams   { unSimpleNgrams   :: Ngrams       }
 instance Hashable ExtractedNgrams
 
 -- | A typeclass that represents extracting ngrams from an entity.
-class HasText h => ExtractNgrams h where
+class ExtractNgrams h where
   extractNgrams :: NLPServerConfig
                 -> TermType Lang
                 -> h

src/Gargantext/Database/Admin/Types/Hyperdata/Contact.hs

@@ -43,7 +43,7 @@ instance NFData HyperdataContact where
 
 instance HasText HyperdataContact
   where
-    hasText = undefined
+    hasText = mempty
 
 defaultHyperdataContact :: HyperdataContact
 defaultHyperdataContact =