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/url.c

@@ -107,7 +107,6 @@
 #include "telnet.h"
 #include "tftp.h"
 #include "http.h"
-#include "http2.h"
 #include "file.h"
 #include "curl_ldap.h"
 #include "vssh/ssh.h"
@@ -117,6 +116,8 @@
 #include "curl_rtmp.h"
 #include "gopher.h"
 #include "mqtt.h"
+#include "rtsp.h"
+#include "smtp.h"
 #include "ws.h"
 
 #ifdef USE_NGHTTP2