make clean: no longer regenerate source

Regenerating code with `make clean` was somewhat useful when only Go code
was generated, because that didn't include the version number / git hash.
The Python and JS code do have that version/hash, so `make clean` became
a source-altering operation, which wasn't nice.

Makefile

@@ -130,8 +130,6 @@ test:
 clean:
 	@go clean -i -x
 	rm -f flamenco*-v* flamenco-manager flamenco-worker *.exe flamenco-*_race
-	rm -f pkg/api/*.gen.go internal/*/mocks/*.gen.go internal/*/*/mocks/*.gen.go
-	@$(MAKE) generate
 
 package: flamenco-manager flamenco-worker
 	mkdir -p dist