Remove unnecessary PCRE2 dependency on R 3.x

For more details on PCRE2 usage in R 3.x, see:
7d25524f8b/m4/R.m4 (L3056-L3058)
7d25524f8b/m4/R.m4 (L3139-L3155)

builder/package.ubuntu-2004

@@ -4,6 +4,12 @@ if [[ ! -d /tmp/output/ubuntu-2004 ]]; then
   mkdir -p /tmp/output/ubuntu-2004
 fi
 
+# R 3.x requires PCRE1
+pcre_lib='libpcre2-8-0'
+if [[ "${R_VERSION}" =~ ^3 ]]; then
+  pcre_lib='libpcre3'
+fi
+
 fpm \
   -s dir \
   -t deb \
@@ -34,8 +40,7 @@ fpm \
   -d libpango-1.0-0 \
   -d libpangocairo-1.0-0 \
   -d libpaper-utils \
-  -d libpcre2-8-0 \
-  -d libpcre3 \
+  -d ${pcre_lib} \
   -d libpng16-16 \
   -d libreadline8 \
   -d libtcl8.6 \