Revert "[clang-format] Keep protobuf "package" statement on one line"

This reverts commit r356835. This patch causes a regression, see the
test below:

verifyFormat("// Detached comment\n\n"
             "// Leading comment\n"
             "syntax = \"proto2\"; // trailing comment\n\n"
             "// in foo.bar package\n"
             "package foo.bar; // foo.bar package\n");

llvm-svn: 356912