tree-wide: drop _pure_ + _const_ from local, static functions

This is supposed to be a help for compilers to apply optimizations on
functions where they can't determine whether they are const/pure on
their own. For static, local functions the compiler can do this on its
own easily however, hence the decoration with pure/const is just noise.
Let's drop it, and let the compiler to its thing better.

(Use it for exported functions, since compilers can't 'reach-over' into
other modules to determine if they are pure, except if LTO is used)

src/basic/fd-util.c

@@ -191,7 +191,7 @@ int fd_cloexec_many(const int fds[], size_t n_fds, bool cloexec) {
         return ret;
 }
 
-_pure_ static bool fd_in_set(int fd, const int fdset[], size_t n_fdset) {
+static bool fd_in_set(int fd, const int fdset[], size_t n_fdset) {
         assert(n_fdset == 0 || fdset);
 
         for (size_t i = 0; i < n_fdset; i++) {

src/basic/prioq.c

@@ -213,7 +213,7 @@ static void remove_item(Prioq *q, struct prioq_item *i) {
         }
 }
 
-_pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
+static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
         struct prioq_item *i;
 
         assert(q);