Simplify the code for most linters and tests with closures

ale_linters/cpp/flawfinder.vim

@@ -6,17 +6,11 @@ call ale#Set('cpp_flawfinder_options', '')
 call ale#Set('cpp_flawfinder_minlevel', 1)
 call ale#Set('c_flawfinder_error_severity', 6)
 
-function! ale_linters#cpp#flawfinder#GetExecutable(buffer) abort
-   return ale#Var(a:buffer, 'cpp_flawfinder_executable')
-endfunction
-
 function! ale_linters#cpp#flawfinder#GetCommand(buffer) abort
-
    " Set the minimum vulnerability level for flawfinder to bother with
    let l:minlevel = ' --minlevel=' . ale#Var(a:buffer, 'cpp_flawfinder_minlevel')
 
-   return ale#Escape(ale_linters#cpp#flawfinder#GetExecutable(a:buffer))
-   \  . ' -CDQS'
+   return '%e -CDQS'
    \  . ale#Var(a:buffer, 'cpp_flawfinder_options')
    \  . l:minlevel
    \  . ' %t'
@@ -25,7 +19,7 @@ endfunction
 call ale#linter#Define('cpp', {
 \  'name': 'flawfinder',
 \  'output_stream': 'stdout',
-\  'executable_callback': 'ale_linters#cpp#flawfinder#GetExecutable',
+\  'executable_callback': ale#VarFunc('cpp_flawfinder_executable'),
 \  'command_callback': 'ale_linters#cpp#flawfinder#GetCommand',
 \  'callback': 'ale#handlers#flawfinder#HandleFlawfinderFormat',
 \})