Remove internal FindESMF.cmake file, use FindESMF.cmake file installed with ESMF

[danrosen25]

EMC is suggesting that we remove the internal FindESMF.cmake file and use the FindESMF.cmake file included with an ESMF installation
NOAA-EMC#2

This can be done by providing the location of the esmf.mk file, which points to the location of the ESMF cmake modules using the ESMF_CMAKEDIR variable. This variable's value can be prepended to the CMAKE_MODULE_PATH list. EMC is specially using ESMF_ROOT to find the FindESMF.cmake file. The advantage of this is that the FindESMF.cmake file does not have to be maintained by the CFBM team.

Suggested by @DusanJovic-NOAA