Removing path to system clang builtin headers

YCM ships clang builtin headers for libclang.

cpp/ycm/.ycm_extra_conf.py

@@ -88,8 +88,6 @@ flags = [
 '-isystem',
 '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1',
 '-isystem',
-'/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.0/include',
-'-isystem',
 '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include',
 ]