examples: uncomment custom search example
examples: uncomment custom search example

This was previously blocking a build. This commit just uncommented
the code.

Fixes: #469
Change-Id: I9a39a5b227be5e28b17a5ebc8f40a436796304e3
Reviewed-on: https://code-review.googlesource.com/c/google-api-go-client/+/55190
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Tyler Bui-Palsulich <b41e4aa57d2ad7eb1b29835a1b483e209dcc3c0e@google.com>

google/google-api-go-client,googleapis/google-api-go-client,google/google-api-go-client,googleapis/google-api-go-client