Do not echo diagnostics in virtual-text when update_diagnostics_in_insert_mode == 0

Needed settings:

let g:ycm_update_diagnostics_in_insert_mode = 0
let g:ycm_echo_current_diagnostic = 'virtual-text'

Previously, whenever we should NOT display diagnostic UI, but diag
message would not need clearing, we ended up echoing. Most noticable in
the following example

int main() {
	puts("")<CR>
}

Note that this first patch still leaves a diagnostic UI flicker on
InsertLeave.

Author: bstaletic

python/ycm/diagnostic_interface.py

@@ -44,8 +44,7 @@ def OnCursorMoved( self ):
     if self._user_options[ 'echo_current_diagnostic' ]:
       line, _ = vimsupport.CurrentLineAndColumn()
       line += 1  # Convert to 1-based
-      if ( not self.ShouldUpdateDiagnosticsUINow() and
-           self._diag_message_needs_clearing ):
+      if not self.ShouldUpdateDiagnosticsUINow():
         # Clear any previously echo'd diagnostic in insert mode
         self._EchoDiagnosticText( line, None, None )
       elif line != self._previous_diag_line_number: