Is it good idea to remove dash from a GUID?

Yes, it is OK to remove the dashes. The uniqueness of the Guid is guaranteed.

Dashes are only for readability: internally the Guid is made of 16 bytes.
You can see Microsoft and Wikipedia for more details.
Take a look at constructors too:

public Guid(int a, short b, short c, byte[] d);
public Guid(int a, short b, short c, byte d, 
            byte e, byte f, byte g, byte h, 
            byte i, byte
public Guid(uint a, ushort b, ushort c, byte d, 
            byte e, byte f, byte g, byte h, 
            byte i, byte j, byte k);

The dashes are always in the same place, so no, it will not reduce the uniqueness.

System.Guid.NewGuid().ToString("N");

Will generate a GUID without dashes, as in this documentation