[Java] Remove Gradle caching from macOS build since it overflows allowed limits

See https://github.com/real-logic/simple-binary-encoding/runs/372121366, e.g.: ``` Post job cleanup. /usr/bin/tar -cz -f /Users/runner/runners/2.163.1/work/_temp/7ec94d5c-8369-467d-ae86-dc123a967837/cache.tgz -C /Users/runner/.gradle/wrapper . [warning]Cache size of ~2187 MB (2293228503 B) is over the 400MB limit, not saving cache. ```

Author: vyazelenko

.github/workflows/ci.yml

@@ -146,20 +146,6 @@ jobs:
  CC: clang
  CXX: clang++
  steps:
- - name: Checkout code
- uses: actions/checkout@v2
- - name: Cache Gradle dependencies
- uses: actions/cache@v1
- with:
- path: ~/.gradle/caches
- key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
- restore-keys: |
- ${{ runner.os }}-gradle-
- - name: Cache Gradle wrappers
- uses: actions/cache@v1
- with:
- path: ~/.gradle/wrapper
- key: ${{ runner.os }}-gradle-wrapper
  - name: Install compiler
  run: |
  sudo xcode-select -switch /Applications/Xcode_${{ matrix.version }}.app