Clean up single namespace forward-declarations

Done using the following ruby script:

Dir.glob('**/*.h').each { |file|
  if File.file?(file)
    s = File.read(file)
    t = s.gsub(/^namespace .+ \{\n\s*class .*;\n\s*\}.*$/) { |m| m.gsub(/\n\s*/, ' ').gsub(/\s*\/\/.*$/, '') }
    if t != s
      puts file
      File.open(file, 'w').write(t)
    end
  end
}

Change-Id: Iffcb966e90eb8e1a625eccd5dd0b94f000ae368e
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/git/gitclient.h

@@ -47,9 +47,7 @@ class QDebug;
 class QProcessEnvironment;
 QT_END_NAMESPACE
 
-namespace Core {
-    class ICore;
-}
+namespace Core { class ICore; }
 
 namespace VcsBase {
     class Command;
@@ -62,9 +60,7 @@ namespace Utils {
     struct SynchronousProcessResponse;
 }
 
-namespace DiffEditor {
-    class DiffEditor;
-}
+namespace DiffEditor { class DiffEditor; }
 
 namespace Git {
 namespace Internal {