Remove gradle

[jcoyne]

The bundled version is out of date. We should run with Gradle 8 instead. Install via brew install gradle

[jmartin-sul]

according to https://docs.gradle.org/8.4/userguide/gradle_wrapper.html:

The recommended way to execute any Gradle build is with the help of the Gradle Wrapper (referred to as "Wrapper").

and it goes on to list some pros about consistency of builds between different machines.

i think maybe we should close this PR? the build.gradle part was done in #65, which also upgraded to the latest gradlew scripts and configs. #69 fixes the gradle-wrapper.jar oversight from #65, as well as showing one way to fix the CI build. #66 got rid of gradle/wrapper/dists/gradle-2.13-bin.zip. so i think that covers almost everything happening in this PR. it might still be nice to have a README update about upgrading gradlew locally and checking in the changes if the project hasn't been touched in a while.

i'm also open to getting rid of gradlew if we don't think it'll be beneficial (or beneficial enough to warrant having to update it every so often and check in said updates).