stop to support android/32bit build

[netpyoung]

Current build setting can't build 32bit(armv7) android on Unity2020/2021(what i checked versions) .

Plugin 'Assets/unity.webp/Plugins/Android/libs/armeabi-v7a/libwebpdecoder.so' doesn't have CPU architecture set, since it's a native plugin, valid architecture is required, skipping.
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)
Plugin 'Assets/unity.webp/Plugins/Android/libs/armeabi-v7a/libwebpmux.so' doesn't have CPU architecture set, since it's a native plugin, valid architecture is required, skipping.
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)
Plugin 'Assets/unity.webp/Plugins/Android/libs/armeabi-v7a/libwebpdemux.so' doesn't have CPU architecture set, since it's a native plugin, valid architecture is required, skipping.
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

And I'm not sure the necessity to support android/32bit build. so I will remove native library files armv7.