Remove VPN and tun2socks APIs from the Android library

- Remove tun2socks binaries
- Remove copying tun2socks binaries step from the make file

PsiphonTunnel.java changes:
- Remove VPN related code
- Remove JNI tun2socks code
- Remove target ICS annotations since we are never lower than Android 14
- Reference VpnService classes since we are never lower than ICS
- Remove code targeting lower than ICS
- Fix potential NPEs in the network API code
- Run code inspection and perform cleanup
- Update comments

MobileLibrary/Android/PsiphonTunnel/libs/.gitignore

@@ -1 +0,0 @@
-!*.so

MobileLibrary/Android/make.bash

@@ -48,10 +48,6 @@ fi
 mkdir -p build-tmp/psi
 unzip -o psi.aar -d build-tmp/psi
 yes | cp -f PsiphonTunnel/AndroidManifest.xml build-tmp/psi/AndroidManifest.xml
-yes | cp -f PsiphonTunnel/libs/armeabi-v7a/libtun2socks.so build-tmp/psi/jni/armeabi-v7a/libtun2socks.so
-yes | cp -f PsiphonTunnel/libs/arm64-v8a/libtun2socks.so build-tmp/psi/jni/arm64-v8a/libtun2socks.so
-yes | cp -f PsiphonTunnel/libs/x86/libtun2socks.so build-tmp/psi/jni/x86/libtun2socks.so
-yes | cp -f PsiphonTunnel/libs/x86_64/libtun2socks.so build-tmp/psi/jni/x86_64/libtun2socks.so
 mkdir -p build-tmp/psi/res/xml
 yes | cp -f PsiphonTunnel/ca_psiphon_psiphontunnel_backup_rules.xml build-tmp/psi/res/xml/ca_psiphon_psiphontunnel_backup_rules.xml