Remove nusiance output

Stop printing:
```
with diagnostic data "(none provided)"
```
at the end of every assertion failure that didn't provide diagnostic
data. It's pedantic and redundant.

example/invoke-via-macro.F90

@@ -28,6 +28,8 @@ program invoke_via_macro
     print *,'Here comes the expected assertion failure:'
     print *
 #endif
+  !call_assert(1+1>2)
+  !call_assert_describe(1+1>2, "Mathematics is broken!")
   call_assert_diagnose(1+1>2,  "example with array diagnostic data" , intrinsic_array_t([1,1,2])) ! false assertion
 
 end program invoke_via_macro

src/assert/assert_subroutine_s.F90

@@ -31,7 +31,7 @@
         represent_diagnostics_as_string: &
         if (.not. present(diagnostic_data)) then
 
-          trailer = "(none provided)"
+          trailer = ""
 
         else
 
@@ -51,10 +51,11 @@
             class default
               trailer = "of unsupported type."
           end select
+          trailer = ' with diagnostic data "' // trailer // '"'
 
         end if represent_diagnostics_as_string
 
-        error stop header // ' with diagnostic data "' // trailer // '"'
+        error stop header // trailer
 
       end if check_assertion