[android][test] Don't set lit's config.target_env_prefix when running natively on Android

This broke in swiftlang#41741, putting it back the way it was.

Author: finagolfin

test/lit.cfg

@@ -1457,7 +1457,6 @@ elif (run_os in ['linux-gnu', 'linux-gnueabihf', 'freebsd', 'openbsd', 'windows-
       config.target_shared_library_suffix = ".so"
       config.target_sdk_name = "android"
       config.target_cc_options = "-fPIE"
-      config.target_env_prefix = 'ANDROID_CHILD_'
     else:
       lit_config.note("Testing Linux " + config.variant_triple)
       config.target_object_format = "elf"