[Support/MemoryBuffer] Remove the assertion that the file size did not shrink.
[Support/MemoryBuffer] Remove the assertion that the file size did not shrink.

This can happen in practice with the user changing files and we can recover from it.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@208143 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,chubbymaggie/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,chubbymaggie/asap,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm