Android: Remove no-op reference to webapk_proguard_jar_path

Since we enabled r8, this variable is ignored. Stop setting it.

Bug: 908988
Change-Id: I0aa9e3e0a0a6133be81916bf36126bed86aab116
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752292
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Sam Maier <smaier@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686539}

chrome/android/webapk/shell_apk/BUILD.gn

@@ -187,9 +187,6 @@ template("webapk_tmpl") {
     native_lib_placeholders = [ "libfoo.so" ]
 
     if (!is_java_debug) {
-      if (defined(webapk_proguard_jar_path)) {
-        proguard_jar_path = webapk_proguard_jar_path
-      }
       proguard_enabled = true
       proguard_configs = [
         "//chrome/android/webapk/shell_apk/proguard.flags",