bootstrap: remove dead code

The workaround added by commit 04f442f755 (Workaround for short jump
tables on PA-RISC., 2014-11-04, v3.1.0-rc2~7^2) was only partially
removed by commit 6fdcf02aaf (bootstrap: remove dead branches,
2017-08-15, v3.10.0-rc1~250^2~2).  Remove the rest of it.

Also remove an unused check for Linux systems.

bootstrap

@@ -154,9 +154,6 @@ if echo "${cmake_system}" | grep HP-UX >/dev/null 2>&1; then
   https://gitlab.kitware.com/cmake/cmake/-/issues/17137
 
 Use CMake 3.9 or lower instead.'
-  cmake_system_hpux=true
-else
-  cmake_system_hpux=false
 fi
 
 # Determine whether this is AIX
@@ -166,27 +163,6 @@ else
   cmake_system_aix=false
 fi
 
-# Determine whether this is Linux
-if echo "${cmake_system}" | grep Linux >/dev/null 2>&1; then
-  cmake_system_linux=true
-else
-  cmake_system_linux=false
-fi
-
-# Determine whether this is a PA-RISC machine
-# This only works for Linux or HP-UX, not other PA-RISC OSs (BSD maybe?). Also
-# may falsely detect parisc on HP-UX m68k
-cmake_machine_parisc=false
-if ${cmake_system_linux}; then
-  if uname -m | grep parisc >/dev/null 2>&1; then
-    cmake_machine_parisc=true
-  fi
-elif ${cmake_system_hpux}; then
-  if uname -m | grep ia64 >/dev/null 2>&1; then : ; else
-    cmake_machine_parisc=true
-  fi
-fi
-
 # Choose the generator to use for bootstrapping.
 if ${cmake_system_mingw}; then
   # Bootstrapping from an MSYS prompt.