Remove unneeded using Base::capacity in WTF::Vector definition.

Redundant since Vector already defines capacity() as a public method,
and it confuses the Chrome style rewriter.

From C++11 [namespace.udecl/15]:
  When a using-declaration brings names from a base class into a
  derived class scope, member functions and member function templates
  in the derived class override and/or hide member functions and
  member function templates with the same name, parameter-type-list
  (8.3.5), cv-qualification, and ref-qualifier (if any) in a base
  class (rather than conflicting).

BUG=584105

Review URL: https://codereview.chromium.org/1837583002

Cr-Commit-Position: refs/heads/master@{#383415}

third_party/WebKit/Source/wtf/Vector.h

@@ -836,7 +836,6 @@ private:
 
     using Base::m_size;
     using Base::buffer;
-    using Base::capacity;
     using Base::swapVectorBuffer;
     using Base::allocateBuffer;
     using Base::allocationSize;