don't install multiple arm android toolchains

We were using /android/ndk-arm-9 in the buildbot config, but using
/android/ndk-arm in the Dockerfile to set up PATH.  One ARM toolchain is
enough.

Author: froydnj

master/master.cfg

@@ -861,7 +861,7 @@ class ConfigCommand(object):
 
         # Set up the path to the android NDK
         if testing_android:
-            s += " --android-cross-path=/android/ndk-arm-9"
+            s += " --android-cross-path=/android/ndk-arm"
             s += " --disable-docs"
 
         if "release-channel" in props:

slaves/android/install-ndk.sh

@@ -14,12 +14,6 @@ chmod +x android-ndk-r10e-linux-x86_64.bin
 bash android-ndk-r10e/build/tools/make-standalone-toolchain.sh \
         --platform=android-9 \
         --toolchain=arm-linux-androideabi-4.8 \
-        --install-dir=/android/ndk-arm-9 \
-        --ndk-dir=/android/android-ndk-r10e \
-        --arch=arm
-bash android-ndk-r10e/build/tools/make-standalone-toolchain.sh \
-        --platform=android-21 \
-        --toolchain=arm-linux-androideabi-4.8 \
         --install-dir=/android/ndk-arm \
         --ndk-dir=/android/android-ndk-r10e \
         --arch=arm