search: include 'findprevious' and 'findnext' in the tiny version

Thus fix a compilation failure when configured with --enable-tiny.

Now M-Q will be functional also in a tiny nano.

src/proto.h

@@ -487,10 +487,8 @@ void do_search(void);
 void do_search_forward(void);
 void do_search_backward(void);
 void do_research(void);
-#ifndef NANO_TINY
 void do_findprevious(void);
 void do_findnext(void);
-#endif
 void not_found_msg(const char *str);
 void go_looking(void);
 ssize_t do_replace_loop(const char *needle, bool whole_word_only,

src/search.c

@@ -366,7 +366,6 @@ void do_research(void)
 	tidy_up_after_search();
 }
 
-#ifndef NANO_TINY
 /* Search in the backward direction for the next occurrence. */
 void do_findprevious(void)
 {
@@ -380,7 +379,6 @@ void do_findnext(void)
 	UNSET(BACKWARDS_SEARCH);
 	do_research();
 }
-#endif /* !NANO_TINY */
 
 /* Report on the status bar that the given string was not found. */
 void not_found_msg(const char *str)