Do not generate cargo_pkg_version when --no-pkg-vers is passed

If you passed --no-pkg-vers to cargo2android.py, it would still
generate cargo_pkg_version with an empty string.  Instead, simply
don't generate anything.

Test: Use with and without argument.
Change-Id: I544e4789312ccc3481da73c78f0f2cae2ad6619c
diff --git a/scripts/cargo2android.py b/scripts/cargo2android.py
index c0db538..937d777 100755
--- a/scripts/cargo2android.py
+++ b/scripts/cargo2android.py
@@ -648,7 +648,8 @@
       self.dump_srcs_list()
     if self.cargo_env_compat:
       self.write('    cargo_env_compat: true,')
-      self.write('    cargo_pkg_version: "' + self.cargo_pkg_version + '",')
+      if not self.runner.args.no_pkg_vers:
+        self.write('    cargo_pkg_version: "' + self.cargo_pkg_version + '",')
     if 'test' in self.crate_types:
       self.write('    test_suites: ["general-tests"],')
       self.write('    auto_gen_config: true,')
@@ -883,7 +884,8 @@
       self.write('    crate_name: "' + self.crate_name + '",')
     if not self.defaults and self.cargo_env_compat:
       self.write('    cargo_env_compat: true,')
-      self.write('    cargo_pkg_version: "' + self.cargo_pkg_version + '",')
+      if not self.runner.args.no_pkg_vers:
+        self.write('    cargo_pkg_version: "' + self.cargo_pkg_version + '",')
     if not self.default_srcs:
       self.dump_srcs_list()
     if 'test' in self.crate_types and not self.defaults: