RFR: 8224629: Unnecessary indirection in LambdaToMethod

[Alan Malloy]

Hello. Please review this patch to eliminate an unnecessary upcast and
method call in LambdaToMethod.

bug: https://bugs.openjdk.java.net/browse/JDK-8224629
webrev: http://cr.openjdk.java.net/~cushon/8224629/webrev.00/

Testing: All of jtreg:test/langtools/tools/javac pass locally. No new test
added, as no behavior change is intended.

Thanks,
    Alan