feat: adding new mf_deletefile macro (and test)

Also, update to mm_spkexport macro

tests/crossplatform/mf_deletefile.test.sas

@@ -0,0 +1,28 @@
+/**
+  @file
+  @brief Testing mf_deletefile.sas macro
+
+  <h4> SAS Macros </h4>
+  @li mf_deletefile.sas
+  @li mp_assert.sas
+  @li mp_assertscope.sas
+
+**/
+
+%let test1file=&sasjswork/myfile1.txt;
+
+%mf_writefile(&test1file,l1=some content)
+
+%mp_assert(
+  iftrue=(%sysfunc(fileexist(&test1file))=1),
+  desc=Check &test1file exists
+)
+
+%mp_assertscope(SNAPSHOT)
+%mf_deletefile(&test1file)
+%mp_assertscope(COMPARE)
+
+%mp_assert(
+  iftrue=(%sysfunc(fileexist(&test1file))=0),
+  desc=Check &test1file no longer exists
+)