Kernel: Remove KBufferBuilder API for reusing an existing buffer

This is not used anywhere anymore anyway.

Kernel/KBufferBuilder.cpp

@@ -48,14 +48,6 @@ KBufferBuilder::KBufferBuilder(bool can_expand)
 {
 }
 
-KBufferBuilder::KBufferBuilder(RefPtr<KBufferImpl>& buffer, bool can_expand)
-    : m_buffer(buffer)
-    , m_can_expand(can_expand)
-{
-    if (!m_buffer)
-        m_buffer = buffer = KBufferImpl::try_create_with_size(4 * MiB, Region::Access::Read | Region::Access::Write);
-}
-
 void KBufferBuilder::append_bytes(ReadonlyBytes bytes)
 {
     if (!check_expand(bytes.size()))

Kernel/KBufferBuilder.h

@@ -17,7 +17,6 @@ public:
     using OutputType = KBuffer;
 
     explicit KBufferBuilder(bool can_expand = false);
-    explicit KBufferBuilder(RefPtr<KBufferImpl>&, bool can_expand = false);
     KBufferBuilder(KBufferBuilder&&) = default;
     ~KBufferBuilder() = default;