[CMake] Remove extra lldb-framework target

Summary: The custom lldb-framework target was meant to encapsulate all build steps that LLDB.framework needs on top of the ordinaly liblldb. In the end all of it happens in post-build steps, so we can do the same with liblldb and cut down another source of confusion.

Reviewers: xiaobai, JDevlieghere

Reviewed By: xiaobai, JDevlieghere

Subscribers: mgorny, lldb-commits, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D64397

llvm-svn: 365615