refactor(build): remove INCLUDE_GENERATED_DECLARATIONS guards

These are not needed after #35129 but making uncrustify still play nice
with them was a bit tricky.

Unfortunately `uncrustify --update-config-with-doc` breaks strings
with backslashes. This issue has been reported upstream,
and in the meanwhile auto-update on every single run has been disabled.

src/nvim/shada.c

@@ -338,9 +338,7 @@ typedef struct {
   PMap(cstr_t) file_marks;  ///< All file marks.
 } WriteMergerState;
 
-#ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "shada.c.generated.h"
-#endif
+#include "shada.c.generated.h"
 
 #define DEF_SDE(name, attr, ...) \
   [kSDItem##name] = { \