Android: Remove obsolete proguard -keep for content.browser.input

Bug: 636474
Change-Id: I303c9f2f2bd65bf3ba8e7041c72d6ddb75529adf
Reviewed-on: https://chromium-review.googlesource.com/1055609Reviewed-by: Shimi Zhang <ctzsm@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557930}

chrome/android/java/proguard.flags

@@ -26,9 +26,3 @@
 -keepclassmembers class android.support.design.internal.BottomNavigationMenuView {
     boolean mShiftingMode;
 }
-
-# There is stack-walking code in our IME that breaks with obfuscation.
-# https://crbug.com/824048.
--keepnames class org.chromium.content.browser.input.* {
-  *;
-}