Remove makefile comments about switching between JSC and V8

We no longer support JSC.

Also add a check for ARMv7, as this is the only version on which V8 is well
tested. Note that we no longer support ARMv5. See b/6015755.

Note that this was previously landed as
https://android-git.corp.google.com/g/#/c/162145, but broke the build, so was
reverted.

Bug: 5495373
Change-Id: Ibde55183ce8bc3b39e513f8b5d331219e793cf49
diff --git a/Android.mk b/Android.mk
index dcb3ea4..ff42934 100644
--- a/Android.mk
+++ b/Android.mk
@@ -17,14 +17,11 @@
 
 BASE_PATH := $(call my-dir)
 
-# Two ways to control which JS engine is used:
-# 1. use JS_ENGINE environment variable, value can be either 'jsc' or 'v8'
-#    This is the preferred way.
-# 2. if JS_ENGINE is not set, or is not 'jsc' or 'v8', this makefile picks
-#    up a default engine to build.
-#    To help setup buildbot, a new environment variable, USE_ALT_JS_ENGINE,
-#    can be set to true, so that two builds can be different but without
-#    specifying which JS engine to use.
+ifeq ($(TARGET_ARCH),arm)
+    ifneq ($(strip $(ARCH_ARM_HAVE_ARMV7A)),true)
+        $(warning WARNING: Building on ARM with non-ARMv7 variant. On ARM, V8 is well tested only on ARMv7.)
+    endif
+endif
 
 # Build libv8 and v8shell
 ifneq ($(filter $(TARGET_ARCH),x86 arm),)