Revert "Change redundant String#replace..."

This reverts commit a4e37948a2. String#clear is a
method that was introduced in Ruby 1.9, it's not available in 1.8.

lib/pry.rb

@@ -104,7 +104,7 @@ class Pry
   DEFAULT_CONTROL_D_HANDLER = proc do |eval_string, _pry_|
     if !eval_string.empty?
       # clear input buffer
-      eval_string.clear
+      eval_string.replace("")
     elsif _pry_.binding_stack.one?
       # ^D at top-level breaks out of loop
       _pry_.binding_stack.clear

lib/pry/default_commands/editing.rb

@@ -10,7 +10,7 @@ class Pry
       create_command "!", "Clear the input buffer. Useful if the parsing process goes wrong and you get stuck in the read loop.", :use_prefix => false do
         def process
           output.puts "Input buffer cleared!"
-          eval_string.clear
+          eval_string.replace("")
         end
       end
 

lib/pry/pry_instance.rb

@@ -348,7 +348,7 @@ class Pry
     # from within Readline.
     rescue Interrupt
       output.puts ""
-      eval_string.clear
+      eval_string.replace("")
       return
     end