Fix race condition in unit test.

Removing an input stream immediately after it's created causes a race
to read the entire file before the reader gets the signal to stop.

testing/btest/scripts/base/frameworks/file-analysis/input/basic.bro

@@ -23,7 +23,6 @@ event bro_init()
 	local source: string = "../input.log";
 	Input::add_analysis([$source=source, $reader=Input::READER_BINARY,
 	                     $mode=Input::MANUAL, $name=source]);
-	Input::remove(source);
 	}
 
 event file_state_remove(f: fa_file) &priority=-10