build: Remove workaround for ancient libtool

Since libtool 1.5.2, on Linux libtool no longer sets RPATH for any
directories in the dynamic linker search path, so there is no longer an
issue.
This commit reverts a98356f.

configure.ac

@@ -1664,17 +1664,6 @@ AC_CONFIG_SUBDIRS([src/secp256k1])
 
 AC_OUTPUT
 
-dnl Taken from https://wiki.debian.org/RpathIssue
-case $host in
-   *-*-linux-gnu)
-     AC_MSG_RESULT([Fixing libtool for -rpath problems.])
-     sed < libtool > libtool-2 \
-     's/^hardcode_libdir_flag_spec.*$'/'hardcode_libdir_flag_spec=" -D__LIBTOOL_IS_A_FOOL__ "/'
-     mv libtool-2 libtool
-     chmod 755 libtool
-   ;;
-esac
-
 dnl Replace the BUILDDIR path with the correct Windows path if compiling on Native Windows
 case ${OS} in
    *Windows*)