Reland "[cleanup] Remove useless includes."

Reason for reland: Downstream project fixed.

Original change's description:

> [cleanup] Remove useless includes.
>
> Manual cleanup guided by include-what-you-use diagnostic.
>
> Bug: webrtc:8311
> Change-Id: I00be03392cc7ee005101427ea7dc701621ccea68
> Reviewed-on: https://webrtc-review.googlesource.com/c/103320
> Commit-Queue: Yves Gerey <yvesg@webrtc.org>
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25013}

Bug: webrtc:8311
Change-Id: Id6ec4aeb798886a90ace640a190eaf16497ba31b
Reviewed-on: https://webrtc-review.googlesource.com/c/104120
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25034}
diff --git a/rtc_base/sslidentity.cc b/rtc_base/sslidentity.cc
index 823fc38..1d136d7 100644
--- a/rtc_base/sslidentity.cc
+++ b/rtc_base/sslidentity.cc
@@ -11,17 +11,15 @@
 // Handling of certificates and keypairs for SSLStreamAdapter's peer mode.
 #include "rtc_base/sslidentity.h"
 
+#include <string.h>  // for strspn
 #include <ctime>
 #include <string>
-#include <utility>
 
-#include "absl/memory/memory.h"
-#include "rtc_base/checks.h"
-#include "rtc_base/logging.h"
-#include "rtc_base/opensslidentity.h"
-#include "rtc_base/sslfingerprint.h"
-#include "rtc_base/strings/string_builder.h"
-#include "rtc_base/third_party/base64/base64.h"
+#include "rtc_base/checks.h"                     // for FatalLogCall, RTC_DC...
+#include "rtc_base/opensslidentity.h"            // for OpenSSLIdentity
+#include "rtc_base/strings/string_builder.h"     // for StringBuilder
+#include "rtc_base/third_party/base64/base64.h"  // for Base64, Base64::DO_P...
+#include "rtc_base/timeutils.h"                  // for TmToSeconds
 
 namespace rtc {