[build] Always use -j1 for libsnmp to avoid race condition (#8324)

I have been seeing intermittent (~40%) build failures with the same error described in PR #6592, even with that fix present

```
/usr/bin/ld: mibgroup/ip-forward-mib/ipCidrRouteTable/.libs/ipCidrRouteTable_interface.o: file not recognized: file truncated
...
libtool:   error: 'mibgroup/ip-forward-mib/inetCidrRouteTable/inetCidrRouteTable_interface.lo' is not a valid libtool object
make[5]: *** [Makefile:1020: libnetsnmpmibs.la] Error 1
make[5]: *** Waiting for unfinished jobs....
```

#### How I did it

Use `-j1` for the libsnmp build regardless of the value of `$(MULTIARCH_QEMU_ENVIRON)`

#### How to verify it

Performed 10 builds of the libsnmp target (`target/debs/buster/libsnmp-base_5.7.3+dfsg-5_all.deb`) with and without this change. Without the change, hit the error 40% of the time. With the change did not see the error at all

Signed-off-by: Justin Sherman <jusherma@cisco.com>

src/snmpd/Makefile

@@ -29,11 +29,7 @@ $(addprefix $(DEST)/, $(MAIN_TARGET)): $(DEST)/% :
 	stg init
 	stg import -s ../patch-$(SNMPD_VERSION)/series
 
-ifeq ($(MULTIARCH_QEMU_ENVIRON), y)
 	dpkg-buildpackage -rfakeroot -b -d -us -uc -j1 --admindir $(SONIC_DPKG_ADMINDIR)
-else
-	dpkg-buildpackage -rfakeroot -b -d -us -uc -j$(SONIC_CONFIG_MAKE_JOBS) --admindir $(SONIC_DPKG_ADMINDIR)
-endif
 	popd
 
 	mv $(DERIVED_TARGETS) $* $(DEST)/