Debug Info: code clean up.

Since we never insert DIE for DITemplateTypeParameter to a map, there is no need
to call getDIE in getOrCreateTemplateTypeParameterDIE. It is also renamed to
constructTemplateTypeParameterDIE to match with other construct functions
in CompileUnit.

Same applies to getOrCreateTemplateValueParameterDIE.

llvm-svn: 193287