lib: drop unused protocol headers

- drop unused `http.h` includes.
- drop unused `http1.h` include.
- drop unused `http2.h` includes.
- vssh/ssh.h: drop unused `vssh.h` include.
- urldata.h: drop unused protocol includes.
- url: include `smtp.h` directly.
- rtsp.h: include directly where used.
- imap, smtp: drop redundant include, move another from .h to .c.

Verified with an all non-unity CI run.

Closes #20093

lib/vssh/libssh.c

@@ -49,7 +49,6 @@
 #include "../hostip.h"
 #include "../progress.h"
 #include "../transfer.h"
-#include "../http.h"               /* for HTTP proxy tunnel stuff */
 #include "ssh.h"
 #include "../url.h"
 #include "../cfilters.h"

lib/vssh/libssh2.c

@@ -48,7 +48,6 @@
 #include "../hostip.h"
 #include "../progress.h"
 #include "../transfer.h"
-#include "../http.h" /* for HTTP proxy tunnel stuff */
 #include "ssh.h"
 #include "../url.h"
 #include "../cfilters.h"

lib/vssh/ssh.h

@@ -36,8 +36,6 @@
 #include <libssh/sftp.h>
 #endif
 
-#include "vssh.h"
-
 /* meta key for storing protocol meta at easy handle */
 #define CURL_META_SSH_EASY   "meta:proto:ssh:easy"
 /* meta key for storing protocol meta at connection */