[Serve] remove route matching logic from replica

[abrarsheikh]

The correct route value is already part of RequestMetadata after #58180, no need to recompute it again.

no observed perf diff in microbenchmark
After

Type	Name	# Requests	# Fails	Median (ms)	95%ile (ms)	99%ile (ms)	Average (ms)	Min (ms)	Max (ms)	Average size (bytes)	Current RPS	Current Failures/s
GET	/echo?message=hello	28068	0	200	410	470	228.27	80	592	26	430.3	0
Aggregated	28068	0	200	410	470	228.27	80	592	26	430.3	0

Before

Type	Name	# Requests	# Fails	Median (ms)	95%ile (ms)	99%ile (ms)	Average (ms)	Min (ms)	Max (ms)	Average size (bytes)	Current RPS	Current Failures/s
GET	/echo?message=hello	27427	0	210	410	470	232.12	76	604	26	429.7	0
Aggregated	27427	0	210	410	470	232.12	76	604	26	429.7	0