Remove unnecessary definitions in Makefile.PL

These 2 NYTPROF_* targets don't need to be defined outside the scope of
a particular 'make' target.  Defining them may interfere with, e.g.,
.appveyor.yml.

Makefile.PL

@@ -283,8 +283,6 @@ perltidy:
 ctidy_bcpp:
 	bcpp -f 2 -i 4 -bcl -qb 10 -ylcnc -yb NYTProf.xs
 
-NYTPROF_AUTHOR_TESTING=""
-NYTPROF_TEST_SHORT=""
 test_short:
 	NYTPROF_TEST_SHORT=1 NYTPROF_AUTHOR_TESTING=1 make test
 

t/90-pod.t

@@ -1,7 +1,12 @@
 #!perl -w
 
 use Test::More;
-plan skip_all => "NYTPROF_AUTHOR_TESTING only" unless $ENV{NYTPROF_AUTHOR_TESTING};
+unless ($ENV{NYTPROF_AUTHOR_TESTING}) {
+    plan skip_all => "NYTPROF_AUTHOR_TESTING only";
+}
+else {
+    diag("Relevant envvar is true; proceeding to testing POD");
+}
 
 eval "use Test::Pod 1.00";
 plan skip_all => "Test::Pod 1.00 required for testing POD" if $@;