[lldb] Remove debugserver specific string from TestAbortExitCode check

The test only checks the exit code that the debug server sends back, but
not the following explanation which is different for debugserver and lldb-server.

(cherry picked from commit e123959)

Author: Teemperor

lldb/test/Shell/Process/TestAbortExitCode.test

@@ -3,4 +3,4 @@ UNSUPPORTED: system-windows
 RUN: %clang_host %p/Inputs/abort.c -o %t
 RUN: %lldb %t -o run -o continue | FileCheck %s
 
-CHECK: status = 6 (0x00000006) Terminated due to signal 6
+CHECK: status = 6 (0x00000006)