Revert "all: add NDK r12b and set it as default"

This reverts commit 82d09560c6.

It doesn't work - the setup scripts are expecting a ".bin" file (which
is apparently a 7z archive), but what's actually got is a ".zip".

Conflicts:
	buildserver/provision-android-ndk

buildserver/config.buildserver.py

@@ -2,7 +2,6 @@ sdk_path = "/home/vagrant/android-sdk"
 ndk_paths = {
     'r9b': "/home/vagrant/android-ndk/r9b",
     'r10e': "/home/vagrant/android-ndk/r10e",
-    'r12b': "/home/vagrant/android-ndk/r12b",
 }
 java_paths = {
     '8': "/usr/lib/jvm/java-8-openjdk-i386",

buildserver/provision-android-ndk

@@ -20,10 +20,5 @@ if [ ! -e $NDK_BASE/r10e ]; then
     mv android-ndk-r10e r10e
 fi
 
-if [ ! -e $NDK_BASE/r12b ]; then
-    7zr x /vagrant/cache/android-ndk-r12b-linux-x86_64.bin > /dev/null
-    mv android-ndk-r12b r12b
-fi
-
 chmod -R a+rX $NDK_BASE/
 find $NDK_BASE/ -type f -executable -print0 | xargs -0 chmod a+x