Do not use regexps to parse simple version strings.

This saves 5-10ms on a JellyBean Samsung Nexus S for the check
to see whether the VM supports multidex natively.

On a newer Samsung S7 phone it saves 0.5 ms.

Test: manually tested on old and new devices.
Bug: 74259172

Change-Id: Ic05645deb5b4b990d07c726aa0fdd5f0cfa5884b