[swarming] Remove hard-coded shared library configs

The isolate_driver automatically adds referenced shared
libraries. They don't need to be listed explicitly.

The hard-coded location blocks the GN transition
as the library location is different in GYP and GN.

BUG=chromium:474921
NOTRY=true

Review-Url: https://codereview.chromium.org/2190543003
Cr-Commit-Position: refs/heads/master@{#38113}

gni/isolate.gni

@@ -66,11 +66,6 @@ template("v8_isolate_run") {
       } else {
         cfi_vptr = "0"
       }
-      if (use_custom_libcxx) {
-        custom_libcxx = "1"
-      } else {
-        custom_libcxx = "0"
-      }
       if (target_cpu == "x86") {
         target_arch = "ia32"
       } else {
@@ -159,8 +154,6 @@ template("v8_isolate_run") {
         "--config-variable",
         "target_arch=$target_arch",
         "--config-variable",
-        "use_custom_libcxx=$custom_libcxx",
-        "--config-variable",
         "v8_use_external_startup_data=$use_external_startup_data",
         "--config-variable",
         "v8_use_snapshot=$use_snapshot",

gypfiles/isolate.gypi

@@ -80,7 +80,6 @@
         '--config-variable', 'sanitizer_coverage=<(sanitizer_coverage)',
         '--config-variable', 'component=<(component)',
         '--config-variable', 'target_arch=<(target_arch)',
-        '--config-variable', 'use_custom_libcxx=<(use_custom_libcxx)',
         '--config-variable', 'v8_use_external_startup_data=<(v8_use_external_startup_data)',
         '--config-variable', 'v8_use_snapshot=<(v8_use_snapshot)',
       ],

src/base.isolate

@@ -7,13 +7,6 @@
     '../gypfiles/config/win/msvs_dependencies.isolate',
   ],
   'conditions': [
-    ['use_custom_libcxx==1', {
-      'variables': {
-        'files': [
-          '<(PRODUCT_DIR)/lib/libc++.so',
-        ],
-      },
-    }],
     ['v8_use_snapshot=="true" and v8_use_external_startup_data==1', {
       'variables': {
         'files': [