Remove non-source sources from binary targets

No behavior changes.

BUG=chromium:964411

Change-Id: I833cfc4571d2f191acbb53e4b423f2a174ac9de3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/137520
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27978}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 98ff5db..ff9248c 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -1071,7 +1071,6 @@
     "server_socket_adapters.cc",
     "server_socket_adapters.h",
     "sigslot_tester.h",
-    "sigslottester.h.pump",
     "socket_stream.cc",
     "socket_stream.h",
     "test_base64.h",