Update docs links for Avalanche, Celo, and Sei (#2918)

Refresh external documentation links: update the Avalanche C-Chain docs URL to the new /docs/rpcs/c-chain path, replace the Celo DIN link with Infura's Decentralized Infrastructure Service page, and normalize the Sei documentation URLs (remove the redundant www). Documentation-only changes to keep external references current.

Co-authored-by: Ayush Bherwani <ayush.bherwani1998@gmail.com>

Author: shahbaz17

services/reference/avalanche-c-chain/json-rpc-methods/index.md

@@ -16,5 +16,5 @@ Avalanche-specific methods (`avax.*`) that have a dependency on the P-Chain and
 
 :::
 
-Refer to the [Avalanche documentation](https://docs.avax.network/api-reference/c-chain/api) for more
+Refer to the [Avalanche documentation](https://docs.avax.network/docs/rpcs/c-chain) for more
 information about supported methods.

services/reference/celo/index.md

@@ -8,7 +8,7 @@ import CardList from '@site/src/components/CardList'
 
 :::note Decentralized Infrastructure Network (DIN)
 
-Celo is supported through the [DIN](https://www.din.build/) service,
+Celo is supported through the [DIN](https://www.infura.io/solutions/decentralized-infrastructure-service) service,
 meaning calls to the network are routed to [partner infrastructure providers](#partners-and-privacy-policies).
 
 :::

services/reference/sei/index.md

@@ -18,7 +18,7 @@ parallelized EVM architecture, native order matching, and subsystems that addres
 limitations while maintaining Ethereum compatibility.
 
 :::info See also
-Refer to the [official Sei documentation](https://www.docs.sei.io/) for more information.
+Refer to the [official Sei documentation](https://docs.sei.io/) for more information.
 :::
 
 Select an option below to get started with the Sei network.

services/reference/sei/json-rpc-methods/index.md

@@ -9,5 +9,5 @@ sidebar_key: sei-json-rpc-api
 The standard Ethereum methods documented in this section are supported by Infura on the Sei network.
 
 :::info See also
-Refer to the [official Sei documentation](https://www.docs.sei.io/) for more information.
+Refer to the [official Sei documentation](https://docs.sei.io/) for more information.
 :::