Remove NUMBER_OF_COLUMNS and MAX_CELLS_IN_EXTENDED_MATRIX configuration. (#16073)

**What type of PR is this?**
Other

**What does this PR do? Why is it needed?**
This pull request removes `NUMBER_OF_COLUMNS` and
`MAX_CELLS_IN_EXTENDED_MATRIX` configuration.

**Other notes for review**
Please read commit by commit, with commit messages.

**Acknowledgements**
- [x] I have read
[CONTRIBUTING.md](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md).
- [x] I have included a uniquely named [changelog fragment
file](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md#maintaining-changelogmd).
- [x] I have added a description to this PR with sufficient context for
reviewers to understand this PR.

config/params/loader_test.go

@@ -55,6 +55,7 @@ var placeholderFields = []string{
 	"MAX_REQUEST_BLOB_SIDECARS_FULU",
 	"MAX_REQUEST_INCLUSION_LIST",
 	"MAX_REQUEST_PAYLOADS", // Compile time constant on BeaconBlockBody.ExecutionRequests
+	"NUMBER_OF_COLUMNS",    // Configured as a constant in config/fieldparams/mainnet.go
 	"PAYLOAD_ATTESTATION_DUE_BPS",
 	"PROPOSER_INCLUSION_LIST_CUTOFF",
 	"PROPOSER_INCLUSION_LIST_CUTOFF_BPS",