delete dll & links from repo and fix .gitignore

.gitignore

@@ -52,3 +52,8 @@ node_modules/**
 npm-debug.log
 build.sh.meta
 build.bat.meta
+
+# uiwidgets
+Samples/Assets/Plugins/**
+engine/build/**
+engine/third_party/skia

Samples/UIWidgetsSamples_2019_4/Assets/Plugins/x86_64.meta

@@ -1,8 +0,0 @@
-fileFormatVersion: 2
-guid: 33884500f7984174c905ac5cf613ff08
-folderAsset: yes
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Samples/UIWidgetsSamples_2019_4/Assets/Plugins/x86_64/libUIWidgets_d.dll.meta

@@ -1,52 +0,0 @@
-fileFormatVersion: 2
-guid: ef8445888386d7f479b700d769b35a63
-PluginImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  iconMap: {}
-  executionOrder: {}
-  defineConstraints: []
-  isPreloaded: 0
-  isOverridable: 0
-  isExplicitlyReferenced: 0
-  validateReferences: 1
-  platformData:
-  - first:
-      Any: 
-    second:
-      enabled: 1
-      settings: {}
-  - first:
-      Editor: Editor
-    second:
-      enabled: 0
-      settings:
-        CPU: x86_64
-        DefaultValueInitialized: true
-  - first:
-      Standalone: Linux64
-    second:
-      enabled: 1
-      settings:
-        CPU: x86_64
-  - first:
-      Standalone: OSXUniversal
-    second:
-      enabled: 0
-      settings:
-        CPU: x86_64
-  - first:
-      Standalone: Win
-    second:
-      enabled: 0
-      settings:
-        CPU: None
-  - first:
-      Standalone: Win64
-    second:
-      enabled: 1
-      settings:
-        CPU: AnyCPU
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: