[libfuzzer] Removing coverage-related flags from asan options.

[aizatsky]

Summary

Reasons to remove are twofold:

• we don't really need coverage=1 for libfuzzer operation
• makes controlling coverage for fuzzer processes non-trivial.

[kcc]

LGTM

lib/Fuzzer/FuzzerSanitizerOptions.cpp

 //===- FuzzerSanitizerOptions.cpp - default flags for sanitizers ----------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 // Set default options for sanitizers while running the fuzzer.
 // Options reside in a separate file, so if we don't want to set the default
 // options we simply do not link this file in.
 // ASAN options:
-//   * don't dump the coverage to disk.
-//   * enable coverage by default.
 //   * enable handle_abort.
 //===----------------------------------------------------------------------===//
 extern "C" const char *__asan_default_options() {
-  return "coverage_pcs=0:coverage=1:handle_abort=1";
+  return "handle_abort=1";
 }