Add fairsim to gitignore and remove binary (#9439)

## What changed?
Add `fairsim` binary (from #8158) to `.gitignore` and `make clean` and
remove it from the repo. (Don't add it to `make bins` since it's not
generally useful.)

## Why
It accidentally got checked in.

.gitignore

@@ -24,6 +24,7 @@
 /temporal-*
 /tctl*
 /tdbg
+/fairsim
 
 # proto images
 /proto/image.bin
@@ -46,4 +47,4 @@
 **/.ruff_cache/
 
 # Ignoring AI agent files
-.agents/
+.agents/

Makefile

@@ -345,6 +345,7 @@ clean-bins:
 	@rm -f temporal-server-debug
 	@rm -f temporal-cassandra-tool
 	@rm -f tdbg
+	@rm -f fairsim
 	@rm -f temporal-sql-tool
 	@rm -f temporal-elasticsearch-tool