update "radians" to "rad" (#173)

Originator(s): peverwhee

Summary (include the keyword ['closes', 'fixes', 'resolves'] and issue
number):
Update units of "radians" to "rad" to adhere to SI unit conventions
closes #172

Describe any changes made to the namelist: none

List all files eliminated and why: none

List all files added and what they do: none

List all existing files that have been modified, and describe the
changes:
(Helpful git command: git diff --name-status
development...<your_branch_name>)
M   schemes/held_suarez/held_suarez_1994.meta
M   schemes/tj2016/tj2016_sfc_pbl_hs.meta
M   schemes/tropopause_find/tropopause_find.meta
 - update units

List any test failures: none

Is this a science-changing update? New physics package, algorithm
change, tuning changes, etc? no.

schemes/held_suarez/held_suarez_1994.meta

@@ -50,7 +50,7 @@
   intent = in
 [ clat ]
   standard_name = latitude
-  units = radians
+  units = rad
   type = real | kind = kind_phys
   dimensions = (horizontal_loop_extent)
   intent = in

schemes/tj2016/tj2016_sfc_pbl_hs.meta

@@ -121,7 +121,7 @@
   intent = in
 [ clat ]
   standard_name = latitude
-  units = radians
+  units = rad
   type = real | kind = kind_phys
   dimensions = (horizontal_loop_extent)
   intent = in

schemes/tropopause_find/tropopause_find.meta

@@ -65,7 +65,7 @@
   intent = in
 [ lat ]
   standard_name = latitude
-  units = radians
+  units = rad
   type = real | kind = kind_phys
   dimensions = (horizontal_loop_extent)
   intent = in