Remove some duplicated warnings from the big list

configure.ac

@@ -1707,7 +1707,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wbind-to-temporary-copy
      -Wbitfield-constant-conversion
      -Wbool-conversion
-     -Wbool-conversion
      -Wbool-conversions
      -Wbuiltin-requires-header
      -Wchar-align
@@ -1755,7 +1754,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wgnu-array-member-paren-init
      -Wgnu-designator
      -Wgnu-static-float-init
-     -Wgnu-static-float-init
      -Wheader-guard
      -Wheader-hygiene
      -Widiomatic-parentheses
@@ -1813,7 +1811,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wnull-arithmetic
      -Wnull-character
      -Wnull-conversion
-     -Wnull-conversion
      -Wnull-dereference
      -Wout-of-line-declaration
      -Wover-aligned
@@ -1842,7 +1839,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wshift-overflow=2
      -Wshift-sign-overflow
      -Wshorten-64-to-32
-     -Wshorten-64-to-32
      -Wsizeof-array-argument
      -Wsource-uses-openmp
      -Wstatic-float-init
@@ -1895,8 +1891,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wvexing-parse
      -Wvisibility
      -Wvla-extension
-     -Wvla-extension
-     -Wzero-length-array
      -Wzero-length-array
   ], [ TOR_CHECK_CFLAGS([warning_flag]) ])