Remove unnecessary transport requires

The transports are already required by `require 'mcp'`:
https://github.com/modelcontextprotocol/ruby-sdk/blob/v0.3.0/lib/mcp.rb#L16-L17

Author: koic

README.md

@@ -178,7 +178,6 @@ If you want to build a local command-line application, you can use the stdio tra
 
 ```ruby
 require "mcp"
-require "mcp/server/transports/stdio_transport"
 
 # Create a simple tool
 class ExampleTool < MCP::Tool

examples/http_server.rb

@@ -2,7 +2,6 @@
 
 $LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
 require "mcp"
-require "mcp/server/transports/streamable_http_transport"
 require "rack"
 require "rackup"
 require "json"

examples/stdio_server.rb

@@ -2,7 +2,6 @@
 
 $LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
 require "mcp"
-require "mcp/server/transports/stdio_transport"
 
 # Create a simple tool
 class ExampleTool < MCP::Tool

examples/streamable_http_server.rb

@@ -2,7 +2,6 @@
 
 $LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
 require "mcp"
-require "mcp/server/transports/streamable_http_transport"
 require "rack"
 require "rackup"
 require "json"