Summary:
With the release of OpenNSA (https://github.com/Broadcom-Network-Switching-Software/OpenNSA), we can stop using opennsal altogether!

This diff was created using following steps:

cd fboss/agent
find . ! -path "*\/oss*" -type f \( ! -iname "*TARGETS*" \) -exec sed -i -e 's/opennsl_spl_//g' {} \;
find . ! -path "*\/oss*" -type f \( ! -iname "*TARGETS*" \) -exec sed -i -e 's/opennsl/bcm/g' {} \;
find . ! -path "*\/oss*" -type f \( ! -iname "*TARGETS*" \) -exec sed -i -e 's/OPENNSL/BCM/g' {} \;
find . ! -path "*\/oss*" -type f \( ! -iname "*TARGETS*" \) -exec sed -i -e 's/OpenNSL/Bcm/g' {} \; # for symbols like snmpBcmTransmittedPkts2048to4095Octets

Furthermore:

- In all TARGETS under fboss/agent replace wrapped_opennsl_symbols with wrapped_bcm_symbols.
- hg mv agent/facebook/test/OpenNSLInterface.h agent/facebook/test/BcmInterface.h
- BcmEgress.cpp remove operator== overload for opennsl API altogether, and remove operator== BCM API version from inside unnamed namespace, and put it in fboss namespace.
- BcmCinter.h and BcmCinter.cpp now have some duplicate definitions as opennsl_ got renamed to bcm_. Delete one of the definitions "as appropriate".
- Similarly, remove duplicate definitions in FakeSdk.h and FakeSdk.cpp
- Similarly, remove duplicate definitions in SdkTracer.cpp (remove definitions calling CALL_WRAPPERS_RV_NO_CINTER). And lastly, remove CALL_WRAPPERS_RV_NO_CINTER itself.
- arc lint
- Remove OpennslCompatTests.cpp
- Fix ./agent/hw/bcm/tests/facebook/BcmEgressTest.cpp to have #include
  "fboss/agent/facebook/test/MockOpenNSL.h" instead of MockBcm.h

TODO:
- This patch retains the directory structure (facebook/ subdirectory), which will be fixed in subsequent patches.
- Remove opennsl references from TARGETS file, additional cleanup etc.
- Remove all oss directories...

Differential Revision: D16401189

fbshipit-source-id: 607b6c0f97ffcacf3707f6b7a4c9454cc0b24476