Enable always true assert checks in Travis

.dscanner.ini

@@ -63,6 +63,6 @@ auto_ref_assignment_check="disabled" ; FIXME
 ; Checks for incorrect infinite range definitions
 incorrect_infinite_range_check="enabled"
 ; Checks for asserts that are always true
-useless_assert_check="disabled"; FIXME
+useless_assert_check="skip-unittest"
 ; Check for unclear lambda syntax
 lambda_return_check="enabled"

std/algorithm/sorting.d

@@ -880,7 +880,7 @@ template multiSort(less...) //if (less.length > 1)
         }
 
         static if (funs.length == 0)
-            assert("No sorting predicate provided");
+            static assert(false, "No sorting predicate provided for multiSort");
         else
         static if (funs.length == 1)
             return sort!(funs[0], ss, Range)(r);

std/bitmanip.d

@@ -3864,7 +3864,7 @@ private uint countBitsSet(T)(T value) @nogc pure nothrow
     }
     else
     {
-        static assert("countBitsSet only supports 1, 2, 4, or 8 byte sized integers.");
+        static assert(false, "countBitsSet only supports 1, 2, 4, or 8 byte sized integers.");
     }
     return cast(uint)c;
 }