remove PROP_QTAGUID_ENABLED

Remaining hits:
  $ repo grep 'net.qtaguid_enabled|PROP_QTAGUID_ENABLED' | egrep -v '^external/cpuinfo/test/mock/'
  art/Binary file tools/ahat/etc/L.hprof matches
  cts/Binary file tools/release-parser/tests/resources/boot-framework.art matches
  external/cpuinfo/test/dmesg/oppo-r9.log:2212:<14>[   12.785966] (6)[1:init]init: [PropSet]: pid:887 uid:1000 gid:1000 set net.qtaguid_enabled=1
  prebuilts/runtime/appcompat/hiddenapi-flags.csv:412141:Lcom/android/server/NetworkManagementSocketTagger;->PROP_QTAGUID_ENABLED:Ljava/lang/String;,blocked

Bug: 161325508
Test: atest, TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ifa30a7549396312a970fc07c37e8fa8ed85abec0