Remove use_ibus variable from gyp file.

build/linux/system.gyp

Index: build/linux/system.gyp
diff --git a/build/linux/system.gyp b/build/linux/system.gyp
index fa9aee6e08e594fb9f565192eb321c1313cefe7d..4b3ab39a8d5f73a65f614ea066e225bc1ff1c4e3 100644
--- a/build/linux/system.gyp
+++ b/build/linux/system.gyp
@@ -801,31 +801,6 @@
       },
     },
     {
-      'target_name': 'ibus',
-      'type': 'none',
-      'conditions': [
-        ['use_ibus==1', {
-          'variables': {
-            'ibus_min_version': '1.3.99.20110425',
-          },
-          'direct_dependent_settings': {
-            'defines': ['HAVE_IBUS=1'],
-            'cflags': [
-              '<!@(<(pkg-config) --cflags "ibus-1.0 >= <(ibus_min_version)")',
-            ],
-          },
-          'link_settings': {
-            'ldflags': [
-              '<!@(<(pkg-config) --libs-only-L --libs-only-other "ibus-1.0 >= <(ibus_min_version)")',
-            ],
-            'libraries': [
-              '<!@(<(pkg-config) --libs-only-l "ibus-1.0 >= <(ibus_min_version)")',
-            ],
-          },
-        }],
-      ],
-    },
-    {
       'target_name': 'udev',
       'type': 'none',
       'conditions': [