Removed duplicated keys from previous.rst

Signed-off-by: Wojciech Gryncewicz <wgryncewicz@antmicro.com>

docs/previous.rst

diff --git a/docs/previous.rst b/docs/previous.rst
index 2c87fcb..887518a 100644
--- a/docs/previous.rst
+++ b/docs/previous.rst
@@ -29,13 +29,9 @@
         process. It stood for the "8th generation" of the SONOS technology
         developed originally by Cypress.
 
-    :lib_process:`s8phrc`
     :lib_process:`s180`
         The name for using 180nm technology on the 130nm process.
 
-
-    :lib_process:`s8phirs`
-
     :lib_process:`s8pfhd`
         The base process.  5 metal layer backend stack, 16V devices, deep
         nwell.