build: Minor cleanups

find_program() defaults to require the program in question, and as
failing to locate it is now fatal, there's no longer a need for
checking whether it was found later.

Spotted by Michael Catanzaro.

data/theme/meson.build

@@ -14,8 +14,7 @@ styles = [
 
 theme_deps = []
 
-if sassc.found()
-  foreach style: styles
+foreach style: styles
   theme_deps += custom_target('style-' + style,
                               input: '@0@.scss'.format(style),
                               output: '@0@.css'.format(style),
@@ -23,5 +22,4 @@ if sassc.found()
                                 sassc, '-a', '@INPUT@', '@OUTPUT@'
                               ],
                               depend_files: theme_sources)
-  endforeach
-endif
+endforeach

meson.build

@@ -138,7 +138,7 @@ endif
 
 mutter_typelibdir = mutter_dep.get_pkgconfig_variable('typelibdir')
 python = find_program('python3')
-sassc = find_program('sassc', required: true)
+sassc = find_program('sassc')
 
 cc = meson.get_compiler('c')