Trying to knock down all of the unknown layer/purpose pairs that are unused in magic but found in SkyWater GDS files and so generate error messages on GDS read-in.

diff --git a/sky130/magic/sky130.tech b/sky130/magic/sky130.tech
index 9d80aea..65892c3 100644
--- a/sky130/magic/sky130.tech
+++ b/sky130/magic/sky130.tech

@@ -2377,6 +2377,7 @@
 #ifndef METAL5
  ignore MET4,VIA3
  ignore MET5,VIA4
+ ignore MET5BLOCK
 #endif
  ignore NPC
  ignore SEALID
@@ -2387,6 +2388,12 @@
  ignore LOWTAPDENSITY
  ignore FILLOBSPOLY
  ignore OUTLINE
+ ignore POLYCUT
+ ignore POLYGATE
+ ignore DIFFCUT
+ ignore HVNWELLID
+ ignore PADDIFFID
+ ignore PADMETALID
 
  layer pnp NWELL,WELLTXT,WELLPIN
  and PNPID
@@ -4015,7 +4022,15 @@
  calma LOWTAPDENSITY 81 14
  # ESD area ID
  calma ESDID 81 19
+ # Various unused layers
  calma OUTLINE 236 0
+ calma POLYCUT 66 14
+ calma POLYGATE 66 9
+ calma DIFFCUT 65 14
+ calma HVNWELLID 81 63
+ calma MET5BLOCK 72 10
+ calma PADDIFFID 81 6
+ calma PADMETALID 81 8
  
  # LICON
  calma CONT 66 44