EGL BlobCache: Disable multifile to address Wembley perf

Need to investigate multifile performance on Wembley, which does
not use SkiaVk.  That means many small/simple GL programs are taking
longer to start.  Accessing the filesystem is taking longer than a
quick return from a sub 1MB cache.

Test: Build and inspect cache locally
Test: /data/nativetest64/EGL_test/EGL_test
Bug: b/263574392
Change-Id: Iacc725f902fd91c7cbd06b293ec96f5ab5eeb1c3