fix(program_units_and_procedures.md): correct by mdl

Markdownlint identified an instance of multiple blank lines;
this is corrected.

Signed-off-by: Norwid Behrnd <nbehrnd@yahoo.com>

Author: nbehrnd

source/learn/f95_features/program_units_and_procedures.md

@@ -76,7 +76,6 @@ The names of program units and external procedures are *global*, and the
 names of implied-DO variables have a scope of the statement that
 contains them.
 
-
 ## Modules
 
 Modules are used to package