test: don't force bzlmod example to use Bazel 6.0 (#1695)

The minimum version for the bzlmod example is controlled by the CI
config, which uses 6.4

examples/bzlmod/.bazelversion

diff --git a/examples/bzlmod/.bazelversion b/examples/bzlmod/.bazelversion
deleted file mode 100644
index 09b254e..0000000
--- a/examples/bzlmod/.bazelversion
+++ /dev/null
@@ -1 +0,0 @@
-6.0.0