Remove referencing in unit test for arista7800 (#10738)

Signed-off-by: Neetha John [email protected]

Why I did it
Address build failures due to sonic config engine unit tests failing. Failures are due to referencing format used in Arista 7800 sample output for buffer template

How I did it
Remove referencing format

How to verify it
Sonic config engine wheel should be built successfully

Author: neethajohn