remove deleted test target

tools/test_everything.py

@@ -26,7 +26,6 @@
   '//...',
   '@at_clifford_icestorm//...',
   '@at_clifford_yosys//...',
-  '@com_github_westes_flex//...',
   '@com_github_fmtlib_fmt//...',
   '@com_github_gabime_spdlog//...',
   '@com_github_libbacktrace//...',