NaCl/GYP: remove references to prep_toolchain.

ui/events/latency_info_nacl.gyp

 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
    '../../build/common_untrusted.gypi',
   ],
   'conditions': [
     ['disable_nacl==0 and disable_nacl_untrusted==0', {
       'targets': [
         {
           'target_name': 'latency_info_nacl',
           'type': 'none',
           'defines': [
             'EVENTS_BASE_IMPLEMENTATION',
             'EVENTS_IMPLEMENTATION',
           ],
           'include_dirs': [
             '../..',
           ],
           'dependencies': [
             '../../base/base_nacl.gyp:base_nacl',
             '../../base/base_nacl.gyp:base_nacl_nonsfi',
             '../../ipc/ipc_nacl.gyp:ipc_nacl',
             '../../ipc/ipc_nacl.gyp:ipc_nacl_nonsfi',
-            '../../native_client/tools.gyp:prep_toolchain'
           ],
           'variables': {
             'nacl_untrusted_build': 1,
             'nlib_target': 'liblatency_info_nacl.a',
             'build_glibc': 0,
             'build_newlib': 0,
             'build_irt': 1,
             'build_pnacl_newlib': 0,
             'build_nonsfi_helper': 1,
           },
@@ skipping 36 matching lines @@
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }