Simplify print preview system dialog message

print_preview_ui.cc previously specified different specified a system
print dialog shortcut message of "(Ctrl+Shift+P)" for Windows and
ChromeOS, and "(Shift+Ctrl+P)" for everything else except Mac OSX. These
have been unified such that everything besides Mac OSX uses
"(Ctrl+Shift+P)".

Review-Url: https://codereview.chromium.org/2534733002
Cr-Commit-Position: refs/heads/master@{#434915}
1 file changed