Android: Always use LLVM 7, delete build files for LLVM 3

C++ 11 is in heavy use by SwiftShader now, so SwiftShader is now unsupported for Android versions earlier than M.

Bug: b/130460252
Bug: b/130343040
Bug: b/130361288
Change-Id: Idfb64c3fa82325641cc2170f494260c1b5b1eeb4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28988
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: Lingfeng Yang <lfy@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
diff --git a/Android.bp b/Android.bp
index d743770..9a6f9c1 100644
--- a/Android.bp
+++ b/Android.bp
@@ -106,6 +106,6 @@
 subdirs = [
     "src",
     "third_party/llvm-subzero",
-    "third_party/LLVM",
+    "third_party/llvm-7.0",
     "third_party/subzero",
 ]