[sonic-cfggen]: Fix sonic-cfggen build failures for armhf (#10132)

Why I did it
amrhf build fails while building sonic-config-engine whl package
https://dev.azure.com/mssonic/be1b070f-be15-4154-aade-b1d3bfb17054/_apis/build/builds/77089/logs/9

The reason for the failure is due to the fact that there is a new line generated at the top of the file in buffer config test cases while building for broadcom based platform and this issue is not seen in Marvell based platforms.

How I did it
Removed the new line for all the buffer test cases as there is no need to add it and accordingly changed the buffer_config.j2 where the new line is generated.

files/build_templates/buffers_config.j2

@@ -131,7 +131,6 @@ def
     {%- if port_names_list_inactive.append(port) %}{%- endif %}
 {%- endfor %}
 {%- set port_names_inactive  = port_names_list_inactive  | join(',') %}
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py2/buffers-dell6100.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py2/buffers-mellanox2410-dynamic.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py2/buffers-mellanox2410.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py2/buffers-mellanox2700.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py3/buffers-dell6100.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py3/buffers-mellanox2410-dynamic.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py3/buffers-mellanox2410.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {

src/sonic-config-engine/tests/sample_output/py3/buffers-mellanox2700.json

@@ -1,4 +1,3 @@
-
 {
     "CABLE_LENGTH": {
         "AZURE": {