Some more trailing whitespace in code blocks

Also remove some leading whitespace in code blocks for consistency

Author: lizmat

doc/Language/nativecall.rakudoc

@@ -388,7 +388,6 @@ for 0..$native-array.elems - 1 -> $position {
     say "Element at position $position is "
           ~ $native-array[ $position ];
 }
-
 =end code
 
 that produces the following output
@@ -526,7 +525,6 @@ function.
 =head3 In your Raku code...
 
 =begin code :skip-test<external dependency>
-
 class AStringAndAnInt is repr("CStruct") {
   has Str $.a_string;
   has int32 $.an_int32;
@@ -551,25 +549,21 @@ C<$.an_int32>. You can always bind native types this way.
 =head3 In your C code...
 
 =begin code :lang<C>
-
 typedef struct a_string_and_an_int32_t_ {
   char *a_string;
   int32_t an_int32;
 } a_string_and_an_int32_t;
-
 =end code
 
 Here's the structure. Notice how we've got a C<char *> there.
 
 =begin code :lang<C>
-
 void init_struct(a_string_and_an_int32_t *target, char *str, int32_t int32) {
   target->an_int32 = int32;
   target->a_string = strdup(str);
 
   return;
 }
-
 =end code
 
 In this function we initialize the C structure by assigning an integer