Tests: Drop broken and now unused RunCMake_TEST_FILE option

We cannot use -DRunCMake_TEST=${RunCMake_TEST_FILE} because test cases
use project(${RunCMake_TEST}) and the project name cannot be a path to a
file.  The parent and grandparent commits removed the only uses of the
option.  Drop it now.

Tests/RunCMake/RunCMake.cmake

@@ -38,9 +38,6 @@ function(run_cmake test)
   if(NOT DEFINED RunCMake_TEST_OPTIONS)
     set(RunCMake_TEST_OPTIONS "")
   endif()
-  if (NOT RunCMake_TEST_FILE)
-    set(RunCMake_TEST_FILE "${test}")
-  endif()
   if(APPLE)
     list(APPEND RunCMake_TEST_OPTIONS -DCMAKE_POLICY_DEFAULT_CMP0025=NEW)
   endif()
@@ -57,7 +54,7 @@ function(run_cmake test)
       COMMAND ${CMAKE_COMMAND} "${RunCMake_TEST_SOURCE_DIR}"
                 -G "${RunCMake_GENERATOR}"
                 -T "${RunCMake_GENERATOR_TOOLSET}"
-                -DRunCMake_TEST=${RunCMake_TEST_FILE}
+                -DRunCMake_TEST=${test}
                 --no-warn-unused-cli
                 ${RunCMake_TEST_OPTIONS}
       WORKING_DIRECTORY "${RunCMake_TEST_BINARY_DIR}"