Remove chunk cache benchmark tests from bench/ directory as chunk cache is no longer supported after tiered storage removal.

Changes needed:

wtperf benchmarks:

•  bench/wtperf/runners/chunk-cache-reads.wtperf — delete file

•  bench/wtperf/runners/chunk-cache-reads-base.wtperf — delete file

workgen benchmarks:

•  bench/workgen/runner/chunkcache_simple.py — delete file

Evergreen configuration:

•  test/evergreen.yml — remove perf-test-chunk-cache task (if exists)

• Verify no other tasks reference these benchmark files

Acceptance criteria:

• All chunk cache benchmark files removed from 
   bench/ directory
• No Evergreen tasks reference chunk cache benchmarks
• Evergreen patch build passes without chunk cache tests
• No references to chunk-cache or chunkcache remain in 
   bench/ directory