device-htc-m8: remove unused entry 'external_storage_install' (MR 4799)

The device info entry 'external_storage_install' is not in use
anymore, remove it.

device/testing/device-htc-m8/APKBUILD

@@ -31,7 +31,7 @@ nonfree_firmware() {
 }
 
 sha512sums="
-c86e8bc74577b6977c42c638df251a116f713bdf4c70582e51d738795813516e72af2a2017ce29d6452d42b4f236d9eeb0e954702f45a9aa4c35949f48c22d76  deviceinfo
+31665a740ef686d6b371c14eb9d13c706b94c3c961158dcfba6a8a572602b49fba4d569003e323380374bb7954fd757cc155bda1aa34e93011d6ed103809e8bf  deviceinfo
 765abaad5fda0dfda5e62e1e48414d3eea822198f39d0792171a04d73f86f6273a6e562afab430cbfcdd084412568a0ad03d012e9c40c5564f5cd1b9c0f181eb  initfs-hook.sh
 f0f69ab3b5b3fed11ec5049f37c71c4e9dcf87dc1f238199a3917dd61957d46783a8798d63d400cc5d3983987e750e3fec6d7117561ad5005f28131ae4821d66  90-android-touch-dev.rules
 "

device/testing/device-htc-m8/deviceinfo

@@ -6,7 +6,6 @@ deviceinfo_name="HTC One M8"
 deviceinfo_manufacturer="HTC"
 deviceinfo_codename="htc-m8"
 deviceinfo_year="2014"
-deviceinfo_external_storage_install="true"
 deviceinfo_arch="armv7"
 
 # Device related