SpringBoot Remove unused private methods

Hi,

this PR removes a couple of unused private methods.

Cheers, Christoph

Comment From: scottfrederick

FlywayAutoConfiguration.hasAtLeastOneLocation can be removed in 2.7.x (see https://github.com/spring-projects/spring-boot/commit/9821cdfd8b3c62b0eb46505db6f03c6f342fbd4d), the other two unused methods can be removed in main.