Don’t clear commands after specs

Commands are typically registered once at eval time. Clearing them
means that commands aren’t available except in the first spec.

spec/spec-helper.coffee

@@ -121,8 +121,6 @@ beforeEach ->
   addCustomMatchers(this)
 
 afterEach ->
-  atom.commands.clear()
-
   atom.packages.deactivatePackages()
   atom.menu.template = []
 

src/command-registry.coffee

@@ -178,9 +178,6 @@ class CommandRegistry
       break if propagationStopped
       currentTarget = currentTarget.parentNode
 
-  clear: ->
-    @listenersByCommandName = {}
-
 class CommandListener
   constructor: (@selector, @callback) ->
     @specificity = (SpecificityCache[@selector] ?= specificity(@selector))