cros_build_lib: Delete `GetInput` helper

This helper function existed solely for py2/3 compatibility and no longer
needs to exist.

BUG=b:187789302, b:191489806
TEST=`run_tests`

Change-Id: I2e7505e6890911d9282627aa9e9d9c4b6515abca
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2964658
Tested-by: Chris McDonald <cjmcdonald@chromium.org>
Auto-Submit: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cidb_admin.py b/scripts/cidb_admin.py
index 921944b..0a3161e 100644
--- a/scripts/cidb_admin.py
+++ b/scripts/cidb_admin.py
@@ -77,7 +77,7 @@
     cros_build_lib.Die('No command or unsupported command. Exiting.')
 
   print(warn)
-  conf_string = cros_build_lib.GetInput('(%s)?: ' % positive_confirmation)
+  conf_string = input('(%s)?: ' % positive_confirmation)
   if conf_string != positive_confirmation:
     cros_build_lib.Die('You changed your mind. Aborting.')