Update escaping in Android.bp files

Strings like cflags in Android.bp files are parsed by blueprint,
written to build.ninja files, parsed by ninja, and then passed to
/bin/sh -c.  This had resulted in a combination of blueprint
(\"), ninja ($$), and shell (\$) escaping being necessary.

Soong has been updated to automatically handle ninja and shell
escaping, remove extra escaping from Android.bp files.

Bug: 31221587
Test: m -j
Change-Id: I78003c7a18028d27dff444af7d84901345d323a1