[core] clean up fdlog_st and log_error_st decls

typedef redefinitions may cause issues with older compilers

(The intention behind the decls and defines were done to reduce the
 number of unrelated lines modified for the transition to fdlog_st)

x-ref:
  https://trac.macports.org/ticket/63667
  https://github.com/macports/macports-ports/pull/12658

src/chunk.h

@@ -8,12 +8,13 @@
 
 #include "buffer.h"
 #include "array.h"
+#include "fdlog.h"
 
 /* both should be way smaller than SSIZE_MAX :) */
 #define MAX_READ_LIMIT  (256*1024)
 #define MAX_WRITE_LIMIT (256*1024)
 
-struct fdlog_st;        /*(declaration)*/
+/*(needed until 'struct log_error_st' below replaced with 'log_error_st')*/
 #define log_error_st fdlog_st
 
 typedef struct chunk {

src/fdevent.h

@@ -4,8 +4,6 @@
 
 #include "base_decls.h" /* handler_t */
 
-struct fdlog_st;        /*(declaration)*/
-#define log_error_st fdlog_st
 struct fdevents;        /* declaration */
 typedef struct fdevents fdevents;
 
@@ -48,7 +46,7 @@ struct fdnode_st {
 #define FDEVENT_STREAM_RESPONSE_POLLRDHUP BV(15)
 
 __attribute_cold__
-int fdevent_config(const char **event_handler_name, struct log_error_st *errh);
+int fdevent_config(const char **event_handler_name, log_error_st *errh);
 
 __attribute_cold__
 __attribute_const__
@@ -56,7 +54,7 @@ __attribute_returns_nonnull__
 const char * fdevent_show_event_handlers(void);
 
 __attribute_cold__
-fdevents * fdevent_init(const char *event_handler, int *max_fds, int *cur_fds, struct log_error_st *errh);
+fdevents * fdevent_init(const char *event_handler, int *max_fds, int *cur_fds, log_error_st *errh);
 
 __attribute_cold__
 int fdevent_reset(fdevents *ev); /* "init" after fork() */