Drop custom Git whitespace check attribute

Git does not document a `no-lf-at-eof` attribute.  It was once used
by our custom hooks, but these have been superseded by clang-format.

.gitattributes

@@ -7,13 +7,13 @@
 /*.bash          export-ignore eol=lf
 /.clang-format   export-ignore
 
-*.c              whitespace=tab-in-indent,no-lf-at-eof
-*.h              whitespace=tab-in-indent,no-lf-at-eof
-*.h.in           whitespace=tab-in-indent,no-lf-at-eof
-*.cxx            whitespace=tab-in-indent,no-lf-at-eof
-*.hxx            whitespace=tab-in-indent,no-lf-at-eof
-*.hxx.in         whitespace=tab-in-indent,no-lf-at-eof
-*.txt            whitespace=tab-in-indent,no-lf-at-eof
-*.cmake          whitespace=tab-in-indent,no-lf-at-eof
+*.c              whitespace=tab-in-indent
+*.h              whitespace=tab-in-indent
+*.h.in           whitespace=tab-in-indent
+*.cxx            whitespace=tab-in-indent
+*.hxx            whitespace=tab-in-indent
+*.hxx.in         whitespace=tab-in-indent
+*.txt            whitespace=tab-in-indent
+*.cmake          whitespace=tab-in-indent
 
 *.rst            whitespace=tab-in-indent conflict-marker-size=79